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PostPosted: Fri Dec 16, 2016 9:19 pm 
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I guess I can't put it off any longer, I have to make my own chamber reamer.... I have made a few before, but they have been a basic, single flute design.... I thought that a six-flute style was overly complex for my machining skills, so I decided to try one that uses three flutes.... The starting point is a piece of O1 (Oil Hardening) Drill Rod, I chose a piece of 3/8" diameter.... I chucked it up in my lathe, and carefully turned it down to 0.001" over the groove diameter of my TJ's barrel for the chamber portion.... Using the compound rest set at 1* off parallel with the bed, I then machined a taper from that diameter down about 0.010" smaller at a point 0.2" from the end to create the leade.... The remaining part at the end I machined down for the pilot, so that it would smoothly slide into my barrel blank, and that took about 0.0015" smaller than the measured land diameter.... I tried 0.001" but it was a whisker snug, and you can't afford to have the pilot hang up during the reaming process and damage the rifling.... I then turned the shank down about 0.020" smaller than the chamber so that it wouldn't hang up at full depth.... At this point, the reamer blank looked like this.... The front, pilot section of the reamer is on the right....

Image

If you look closely at the section immediately aft of the pilot section, you will see a step down in diameter, and then a taper where the diameter increases at a 1* angle (per side) until the taper meets the parallel chamber portion, which is 0.006" larger than the pilot diameter.... Of that tapered portion, the first half, right behind the pilot, never touches the barrel.... As the reamer progresses into the breech end of the barrel, the pilot centers the reamer, and eventually the tapered part starts shaving away the lands until they are gone.... At that point, the parallel portion of the reamer enters the bore, and the chamber gets longer, and the leade moves forward in the bore, until you stop machining.... In my case, I will be stopping when the transition between the leade and the chamber is about 1/8" forward of the front of the barrel port.... The exact chamber depth will be determined by when the base of the bullet stops at that point.... with the nose of the bullet partially engaged on, and centered by, the tapered leade.... I want to be able to chamber the bullet easily, yet have the nose started into the rifling....

The next step was to mill the flutes.... I mounted the reamer blank in a 3/8" 5C Collet in a hexagonal holder, and then mounted the holded in the milling attachment on my lathe.... I have a stop on the vice so that I can remove and replace the holder, indexing it 120* each time to get three evenly spaced flutes.... Each flute consists of a milled slot from just behind the pilot to just behind the chamber portion, ending in the shank.... The end of the mill is stopped a few thou past the centerline, so that the angle between the cutting face and the tangent to the circle at that point is just a bit less than 90*.... If you stop right at the center, at 90* to the circle, you get a very smooth cut but extremely slow cutting.... The further you go past the center, the more acute the angle, and the more aggressive the cut.... I use about 0.010" past center on a .30 cal, so on this smaller reamer I used only 0.006" past center for the end of the mill.... The cuts are made up from the bottom of the blank, removing only 0.010" at a time with a 1/8" end mill, using conventional milling, not climb cutting (ie always cutting so that the flutes of the mill are digging into the work as you feed it into the end mill).... I made 5 cuts, so the flutes are 0.050" deep.... Here is a photo of the reamer in the Collet, after the flutes have been cut....

Image

Notice that the flute starts aft of the pilot, at a diameter smaller than the pilot, and in the first half tapers larger in diameter until it reaches the diameter of the chamber, and then straight back to create the parallel chamber.... At the very back, it ends just behind the beginning of the reduced diameter shank.... There are three identical flutes, spaced 120* apart around the reamer.... The next step is to make sure the cutting edges are clean of burrs, and then harden the reamer by heating to Cherry red and quenching in oil.... That is followed by a final polish and tempering in an oven to give the reamer the right balance of hardness and toughness.... It is my plan to show those steps in the next post, assuming I get them done tomorrow....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
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Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
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PostPosted: Fri Dec 16, 2016 9:42 pm 
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Very timely post, I was wondering how to make a reamer to use on the SSP project.


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PostPosted: Sat Dec 17, 2016 3:06 pm 
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Here is the hardening process.... I like using a slow running drill press (mine is ~300 rpm) so that I can heat the reamer evenly.... You don't want to clamp too much in the chuck, to minimize heat loss.... Carefully clean the reamer to remove any oil or grease, and then rub it all over with a bar of soap.... I use Ivory.... If you neglect this step, after hardening it will be coated with a black scale that is hard to remove.... The coating of soap will leave it a dull grey after you wash off the scale.... The jar of oil underneath is simply Canola cooking oil, which works fine for the quenching....

Image

With the drill press running, you need to heat the reamer red hot, including part of the larger stub, which acts like a reservoir to hold some of the heat.... If you don't it may cool too quickly and not get hardened evenly.... I didn't have it quite hot enough when I took the photo below, so reheated before quenching.... If you are using an acetylene torch instead of propane, don't get the inner flame cone too close, it is hot enough to melt the steel (the cutting edges will melt first!) and ruin all your machine work.... You have to heat it to a nice glowing red, at which temperature, steel loses its magnetic properties.... You can test that with a magnet if you want, to make sure it is hot enough.... If it is, the magnet will not be attracted to it at all....

Image

Hold it at this temperature for 20-60 seconds (bigger reamers need longer) to make sure that the temperature is even throughout, and then quench it quickly in the oil.... Make sure you plunge it past the shoulder, so that the entire reamer gets hardened.... In the photo below (taken after) is it not quite deep enough....

Image

Leave it rotating in the oil for about a minute, and then raise it back up.... CAUTION, IT WILL STILL BE HOT ENOUGH TO BURN YOU !!! .... It will be a horrible looking, black, scaly mess, but once cool enough to handle most of that will come off easily.... If you missed a spot with the soap, you will know, because there will be a piece of black scale that has to be sanded off.... At this stage, the steel will be extremely hard and brittle, like glass.... You will NOT be able to scratch it with a file if it is properly hardened.... Do NOT drop in on a concrete floor, as it could shatter.... Obviously, that is no good for our purposes, so we will have to temper it.... I will cover that in the next post....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Dec 17, 2016 4:14 pm 
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After hardening, I removed all the scale and repolished the reamer.... It looked like this....

Image

You will note that while I spun it in the lathe to polish the pilot and shank (and the large stub), I polished the actual leade and chamber reamer lengthwise, just removing the scale.... I didn't want to make it smaller, or dull the cutting edges.... After polishing I then used my wife's oven, set at 480*F, to temper it for an hour.... This changes the molecular structure slightly, making the reamer tougher but not as hard.... After tempering and cooling, it looked like this....

Image

The hardness of the part can be judged somewhat by the colour after tempering.... Using 480*F, which is recommended for reamers, should result in a "dark straw" colour.... but realistically, you may see anything between straw and brown.... The mottling on the reamer portion is not a result of uneven tempering, but rather of incomplete polishing, which realistically won't matter.... All that remains is to carefully hone the cutting edges on the radial surface (the part cut by the end of the mill).... In the upper photo, that is the upper flat portion, that the barrel is rotating TOWARDS.... Do NOT touch the circumference, other than to brush it lightly with 600 grit to remove any microscopic burrs from the honing, or you could make it smaller, and then it would cut the chamber undersize.... If when you go to use the reamer you find it cuts too slowly, you can lightly stone the TRAILING edge of the flute OPPOSITE to the cutting edge, putting a very slight bevel on it.... GO SLOW, as this can change the cutting rate very quickly.... That is the edge in the center of the reamer the upper photo....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Dec 17, 2016 5:55 pm 
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I notice you mention to increase cutting speed you can hone the trailing edge. I can not see any relief for the cutting edge, is this a design feature or is it not necessary to have relief.


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PostPosted: Sat Dec 17, 2016 8:15 pm 
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It is not necessary to have relief on the trailing edge, but adding it increases the speed (depth) of the cut.... It works like a "D-Drill".... in fact a single flute reamer is actually a profiled "C-Drill"....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Dec 17, 2016 8:15 pm 
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Here is the process of machining the chamber.... Ready to start cutting.... I centered the tailstock using two 60* centers, and then used the pilot of the reamer as a reference to center the breech of the barrel in the 4-jaw chuck.... I had preciously faced off the breech square.... Note the cutting oil in the bore, and in the channel of the reamer.... I put one channel at the top as an oil reservoir.... I had already advanced the reamer until it just touched, you can see the shiny mark about 1/3 of the way along the flute where the taper started to touch the rifling, before I took this photo.... I cut at the slowest speed on my lathe, which is 28 RPM....

Image

Once the leade section of the reamer starts to cut, I slowly advance the reamer in stages of about 0.008" (1/12 turn of the tailstock handwheel) and allow two full revolutions of the lathe before continuing.... Every half turn of the handwheel (0.050"), I remove the reamer and clean it and blow any chips out of the bore and add more oil.... The chips are nothing more than metal dust that turns the oil black, they are that fine.... In the photo below, the leade portion of the reamer has already entered the bore, and the parallel chamber section is about to enter....

Image

In the next photo, the flutes are fully inside the barrel.... It is at this point the maximum load has been reached.... If you continue to be careful, you can breathe a sign of relief, the reamer didn't break off inside the bore.... At some point, usually before this point, I have already withdrawn the reamer and chambered a bullet until the nose touches the leade.... By careful measuring you can figure out how deep you need to go.... On this reamer, I am now in 1.10" from the front of the pilot, but the front of the parallel chamber is only inside by 0.40".... I need the back of the bullet even with the front of the TP hole in the receiver, which is 0.50" from the back of the barrel.... From this point on, I use up quite a few bullets in measuring my progress by chambering them, using the end of the pilot on the reamer as the nose of the bolt, and then pushing them back out from the muzzle with a cleaning rod to examine them with a magnifying lense.... This allows you to measure how far to the back of the bullet by counting turns on the tailstock handwheel....Mine is 0.100" per turn, which makes it easy.... Alternately, you can measure from the breech to the back of the bullet directly with the depth pin on calipers....

Image

I ended up needing exactly two more turns to have the nose of the bullet nicely engaged in the leade, yet have no rifling marks on the drive band, when the back of the bullet is 0.50" inside the barrel.... The photo below shows the position of the reamer at full chamber depth....

Image

Basically the chamber is now done.... It turned out that my reamer was slightly undersize in the chamber portion, and bullets sized to 0.217" (the groove diameter) were slightly tight, and picking up marks from the chamber.... I used a piece of 3/16" brass rod with a split in the end, and a bit of 220 grit sandpaper in it, to polish the chamber out another thou so that a bullet sized to the groove diameter loaded smoothly.... If you are going to err on the reamer, better too small than too big, you can always polish the chamber out to the perfect diameter.... Here is a photo of the reamer after use....

Image

You will notice the major wear mark in the center of the flute, that is the portion of the leade that machines off the rifling as you advance the reamer into the barrel.... Behind that are some smaller wear marks where the reamer is rubbing inside the parallel chamber as it advances.... Here is a photo of a bullet and some pellets after chambering so that the back of it is 0.50" from the breech (ie level with the front of the barrel port)....

Image

The top row are JSB Exact pellets.... on the left an 18gr. Heavy, in the middle a 25 gr. Monster, and on the right the new 34 gr. Beast.... You will notice the rifling marks on the head band of each pellet, but the only marks on the skirt are where it has collapsed slightly because skirts are always oversized.... The bullets in the bottom row are the new 30 gr. BBT.... On the left is a bullet sized to 0.217" but unchambered.... while the one on the right has been chambered and then pushed back out.... You can clearly see the rifling marks on the back of the nose where it has engaged about halfway along the leade.... but there are no marks on the drive band (sorry for the glare of the flash).... The parallel chamber ends (and the tapered leade starts) just forward of the front of the rear drive band.... The bullet chambers easily just pushed into the breech by hand with a 3/16" brass rod.... You can feel it engage the leade in the last 1/10" of travel.... Anyway, that is how you chamber a barrel.... As you can see, a chamber properly designed and machined for bullets can easily accept waisted pellets....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Dec 18, 2016 6:58 am 
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The attention to detail in both your post and your machine work is nice to see as usual Bob.

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PostPosted: Sun Dec 18, 2016 1:15 pm 
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I have had a few questions about the flutes on the reamer.... Here is a sketch of the end view.... This drawing is for a conventional lathe, running forward, with the reamer in the tailstock, and viewed looking towards the headstock.... The reamer in this application is fixed, and the barrel is rotating counter-clockwise around the drawing.... The short edges of the flute cutouts are the cutting edges....

Image

This is a generic drawing, where 1.000 is the maximum diameter of the reamer.... The flute cutouts which are milled out are shown in blue.... The short edge is where the end of the mill cut.... the long edge is where the side of the mill cut.... For three flutes, I would not go past 1/2 the radius of the reamer with the side of the mill, or you will weaken it too much.... The end of the mill stops anywhere between the centerline and about 5% of the diameter past the centerline (I have never tried more than that).... The further you go past the centerline, the faster the reamer cuts, but the rougher the finish.... If you use three flutes, they are 120* apart.... You can also make a single flute reamer, the cutout is shown as the dotted blue line.... You basically remove a 90* segment of the circle, and again, taking the end of the mill just past the centerline increases the speed of cut....

I offer no guarantees that you will find this design acceptable.... but I have used a few single flute reamers successfully (but I did break one).... and I made and used my first three point one on this build without issue.... I had my cutting edge only 2.5% below the centerline, and it cut very slowly, the chips were basically just metal dust.... On the other hand, having broken a reamer once, inside a barrel, I was being VERY careful.... I make mine from O-1 Drill Rod, which is hardened after machining by heating red hot and quenching in oil.... The reamer should then be tempered at 480*F, which should result in a dark straw to brown colour....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Mon Dec 19, 2016 10:38 pm 
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Today I finished up the breech end of the barrel.... First of all I "Indexed" the barrel.... Not by shooting it and determining the smallest groups, which is the proper way, but by chucking the breech portion in my lathe and using a dial indicator at the muzzle, I determined which way the barrel "droops", and marked which side would be the bottom so that when installed in the breech the muzzle would be at it's lowest point (6 o'clock).... This has been shown over the years to produce the tightest groups, with the second best groups occurring when the barrel bend is towards the top (12"o'clock).... Barrels tend to straighten out when fired, so if the bend is to the side, not only do the groups tend to be larger, they tend to be wider than high.... With the bend in the barrel in the vertical plane, you have more chance of using a barrel tuner (adjustable weight) to shrink the group size.... Having the bend upwards would help the bullet path intersect the scope centerline better, but I opted for the bottom as 90% of the people who bother to index their barrels prefer that.... Tensioned barrels tend to be less sensitive to barrel indexing, but I decided to do everything I could for accuracy....

Once I knew "which way was up", then I knew where to machine the barrel port, so that was the first job.... I measured the distance from the front of the magazine cutout to the center of the TP hole in the breech, added 1/16" to allow for the barrel protrusion that the MRod magazine needs to clip onto, set the barrel up in my milling attachment, and using an edge finder laid out the exact center of the bottom of the barrel, the correct distance from the breech end and drilled a center hole.... I then enlarged that with a 5/32" mill, and using a 5/16" mill made the spot face where the transfer port will seal.... I then used a 7/32" mill, which is the same diameter as the ID of the transfer port I will be using (and the valve exhaust port) and made a shallow mark in the spot face where the transfer port ID will be.... I changed back to the 5/32" mill, moved the barrel forward 1/32", and plunged the mill back in to make the back of the oblong barrel port.... I then rotated the milling attachment 30* so that I could machine the forward sloping front part of the barrel port.... I carefully positioned the 5/32" mill so that it just tickled the front of the 7/32" ID mark, and milled down until I hit the bore.... This made the barrel port 0.160" wide by 0.270" long, with the back vertical and the front sloping forward from the TP into the bore.... This gives me a barrel port that is the same area as the bore, but only 75% as wide, so that the pellets/bullets will not be damaged when loading.... I then used a 60* countersink to blend the 7/32" hole at the spot face into the 0.16 x 0.27" barrel port, removed the barrel from the lathe, and finished the job up with a small spherical diamond burr in my Dremel.... The result is a smooth transition from the 7/32" barrel port to an oblong, bore area, barrel port....

I then loosely installed the barrel in the receiver, using an MRod magazine to hold the back end in the right location in the magazine notch, and the 5/16" spot face lined up perfectly with the TP hole in the receiver.... I loosely installed the 8 setscrews that will hold the barrel in place, tightening them only enough to put small marks in the barrel.... I then pulled the barrel, mounted it back in the milling attachment, using a 5C Collet in a square holder (against an end stop), and adjusted it until the spot face for the barrel port was perfectly centered.... I then moved the barrel in 3/4", and using a center drill put a witness mark on the barrel, to make sure it lined up perfectly with the setscrew mark, and another one 3/4" further in again.... The two rows of setscrew holes in the receiver are 3/4" and 1-1/2" forward of the transfer port, and on all four sides, 90* apart.... With the barrel in the square collet holder, I could rotate it 90*, and repeat this process, and prove to myself that the shallow holes I was about to drill in the barrel would be where the setscrews were.... Everything looked OK, so I used a 3/16" stub drill and drilled eight 0.030" deep pockets in the barrel for the setscrews to tighten into.... This will prevent the cup-point screws from raising rings on the barrel surface which would damage the inside of the receiver, and can actually jam the barrel into it.... You MUST have spot holes or flats for this reason.... In addition, with my tensioned barrel, I wanted all the screws to carry equal load, and the shallow pockets will mean the side of the setscrew point will be against the pocket, instead of just relying on friction from the ring of the cup point.... This will mean that they will easily share the load of up to 1300 lbs. of tension on the barrel from the Bellevilles at the muzzle....

I reinstalled the barrel, lined up the transfer port and magazine again, and lightly tightened the 8 setscrews into the pockets.... On removing the barrel, I found that the two circular marks from the lower cup-point setscrews were perfectly centered in the pockets, but the other six were to one side or the other (although perfectly centered fore and aft).... I used that small round burr again, and ground off the marks from the setscrews in the other 6 locations.... This moved the recess over towards the point of contact with the end of the setscrew, which would allow it to tighten slightly more on the next trial.... After repeating this procedure a few times, I got completely round, centered rings from the cup-points on all 8 setscrews when they were tightened up.... This means that I don't have to crank a crazy amount of tension into them, which could distort the bore.... but that they will all share in the tension load on the barrel.... It took a bit of extra time, but produce a wonderful result that I have 100% confidence in.... You can see the pocket for the setscrews, and the nicely centered marks from the setscrews, in the photo below....

Image

The last job was to machine the groove for the internal O-ring that seals the bolt.... Before I could do that I had to finish turning down the nose of the bolt so that it fit nicely in the chamber I reamed in the barrel.... I had left it oversize for this purpose.... I usually have problems getting a good fit between the bolt and the barrel, because I always seem to have a slight misalignment of the 1/2" holes in the front and back of the receiver.... but I knew this was the most accurate breech I have made to date, and I was not disappointed.... Once I got a nice sliding fit between the bolt nose and the barrel chamber, I put them both in the receiver, and the bolt functioned well.... I could feel a slight resistance from the bolt touching the inside of the barrel, and there is a shiny mark on one side, but it worked without having to sand one side of the bolt or turn it down smaller, so I was delighted.... I dragged out the specially ground tool I have for making O-ring grooves, it is shown in the above photo.... It allows me to machine a 0.070" wide groove inside the barrel, about 0.040" from the end, to hold the O-ring, in this case a #009.... I slowly increased the depth of the groove until it was 0.060", tried the O-ring and found it wouldn't quite go in place, so I deepened the groove until it would JUST lie flat in the groove.... I tried the bolt, and it slid smoothly through the O-ring.... There is 0.007" of compression on each side of the O-ring with the bolt in place, so I think it will seal fine.... if not, I can always use a 90D O-ring instead of the 70D I tried today....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Dec 20, 2016 9:26 pm 
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I seems to take forever to get all the last little details done on a custom PCP project.... Today's job was to make and install the cocking pin in the bolt and cut the recess for it in the bottom of the receiver.... It took me all afternoon.... The hardest job was to figure out the exact spot it had to go.... The angle relative to the bolt handle was the easy part.... Too far forward the slot for the bolt handle was too short, and the handle would hit the end before the hammer cocked.... Too far aft, and the nose of the bolt wouldn't withdraw far enough to allow me to remove the magazine.... Yeah, I should have made the slot 1/16" longer, but that is a difficult thing to set up to machine once, let alone change it later.... Anyway, I finally figured out where to drill and tap the bolt for the cocking pin, and I tapped it 6-32, with a small flat for the head of the SHCS to tighten against.... Since I originally machined the cocking slot in the receiver with a 3/16" mill, I had to use a 7/32" mill to make it wider for the head of the 6-32 screw.... Once I did that, it slid back and forth fine, but the head didn't stick down far enough to properly engage the cocking pin in the hammer.... Well, it caught it, but only right at the top, which with a strong hammer spring can bend the pin, so I had to make a longer cocking pin for the bolt.... I did that by using Loctite 638 (green) to install a hex nut tight against the screw head, and then turned it down to the same diameter as the screw head.... That caused me more grief, because it was so long I barely had room to make the recess in the bottom of the receiver to clear it when it rotates sideways when you close the bolt without breaking through the side of the receiver.... Yeah, one change becomes two, then four, nothing is as simple as it seems....

Anyway, I laid out and milled the recess in the bottom of the receiver to allow the cocking pin to rotate to the side and pull back when the bolt handle is withdrawn into the J-Slot.... Again, that took multiple passes to give enough clearance without carving away more of the 1/2" diameter bolt channel than I need to.... I had to finish it up by hand, using a spherical burr in my Dremel to get the last bit of clearance for the corner of the head of the cocking pin screw.... Once finished, I tried it and it cocks the gun smoothly, so the day was a success.... Here is a photo of the receiver with the recess and the completed bolt....

Image

You can see there isn't much metal left in the receiver beside the recess, and it's actually a bit thinner than what you see down inside at the height of the corner of the rotated cocking pin where I had to clearance it by hand.... However, the job is done, and I'm closing in on getting ready to fire the first shot....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Dec 21, 2016 6:10 pm 
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Well, today was the day!.... I spent the morning doing the final barrel prep work.... I crowned the muzzle, lapped the bore with JS Bore Paste, and then followed that by a polish with JB Bore Brite.... It now gleams from end to end.... I then installed it into the receiver and installed the bolt.... I slid on the front breech retaining band, and installed the PRod trigger group, then slid the hammer into place and installed my borrowed SSG assembly, which I set to minimum gap.... The last step was to measure the length required for the transfer port, and make one from a piece of 5/16" Teflon rod.... I drilled it out to 7/32", and carefully faced the end off until it was 0.010" longer than the space, so it would have a bit of "crush" to seal properly.... Bolting down the receiver was the last task before firing the first shot.... Well, except to take a photo....

Image

As you can see, I haven't fitted the shroud, or modded the stock yet, those items will come after initial testing and tuning.... The gauge said the regulator setpoint was 1900 psi, so I loaded up a magazine, and tried the 34 gr. JSB Beasts....They fed fine, and the first shot was 867 fps (57 FPE).... Not bad for 1900 psi.... I shot a few of each weight pellet, and then shot the 25.3 gr. Monsters until the velocity started to change, and it actually went up about 20 fps at just under 1800 psi, so the setpoint is a bit lower than the gauge reads (or vice versa).... With the pressure a couple of hundred psi below the setpoint, I was able to increase the regulator adjustment, I turned the screw about 45* CCW, and refilled the lower reservoir.... The gauge now read nearly 2200 psi, so I repeated the procedure with the higher setpoint.... Here are the initial results.... The 18.1 and 25.3 gr. are JSB Heavies and Monsters.... the 27.4 and 29.6 gr. are my new BBT HP and FN cast bullets.... and the 34.1 gr. are the new JSB Beasts....

Image

As you can see, the 18.1 gr. JSB Heavies were Supersonic, accompanied by the typical loud CRACK!!!.... The were the only pellet that shot faster at 2100 psi than at 1800, which tells me that I don't have enough hammer strike at the higher pressure.... Since I am out of adjustment with the QB spring (it is right at coil bind with no gap), I will need to come up with a different spring combination, or forego the SSG and just use the QB spring in a conventional preloaded arrangement for now.... I think I will do the latter, at least until I can establish what the maximum velocities are with the various pellets at the current setpoint.... The BBTs, both HP and FN, exceeded 60 FPE at 1800 psi, and the 25.3 gr Monsters were very close to that.... and it would seem that there is more there if I increase the hammer strike.... That certainly means that the gun is breathing well, with the bore-size porting.... Those are pretty healthy FPE numbers at such a low pressure, so I'm encouraged.... and I'm looking forward to finding out what the limit is at the ~2100 psi setpoint once I add some more hammer strike to find out where the plateau is with the different pellet weights....

Bob

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PostPosted: Fri Dec 23, 2016 5:10 pm 
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I tried four different pressures, each 1/4 turn apart on the regulator adjusting screw, and at each pressure I started at zero gap on the SSG and then increased the gap a turn at a time until the velocity dropped below 600 fps at each pressure.... I then plotted the velocity vs. gap at each pressure, with the following results....

Image

The regulator setpoint dropped about 450 psi for 1/4 turn from 2150 down to 1700, then another 450 down to 1250, and then 350 psi from there for the last 1/4 turn, down to 900 psi.... At the highest pressure, even at zero gap, there is not enough hammer strike to reach the velocity plateau.... At 1700 psi, it is just about on the plateau at zero gap.... In both cases the maximum velocity was supersonic with the 18.1 gr. JSB Heavies.... Breaking Mach 1 on only 1700 psi is pretty impressive.... :o

At 1700 psi, the plateau appears to be at about 1150 fps, the knee of the curve was at about 1-2 turns of gap, and the downslope started at about 3 turns out at ~1000 fps.... At 1250 psi, the plateau was 1051 fps, and the knee of the curve occurred at 3-4 turns of gap, with the downslope starting at about 5 turns out at ~900 fps.... With the pressure at 900 psi, the plateau was 956 fps (37 FPE), the knee occurred at about 5 turns of gap, and the downslope began at about 6 turns of gap, at ~800 fps....

The regulator is very easy to adjust, and 100 psi increments should be relatively easy to obtain.... From 1250 to 2150 psi was 1/2 turn of adjustment, so each "hour" on a clock face would be about 150 psi.... That works out to about 50 psi for each 10 degrees.... The regulator seemed to have good stability, returning to the same setpoint after each shot, as close as I can read the gauge, which is a 3000 psi, 180* sweep, 5% gauge, with 200 psi increments.... I am delighted with the performance of the regulator.... and equally pleased with the ability of this gun to reach 950 fps with 18.1 gr. JSB Heavies at only 900 psi....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Dec 23, 2016 9:21 pm 
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I reset the regulator to 1150 psi, filled to 2000 psi, and shot 10 shots with the 18.1 gr. JSB Heavies with 3 turn of gap on the SSG and recorded the pressure drop.... I then repeated that at 4, 5, and 6 turns of gap, with the following results....

Image

At 3 turns, the average velocity was 1018 fps (42.4 FPE) at an efficiency of 1.28 FPE/CI.... At 4 turns of gap, the average velocity was 1003 fps (40.5 FPE) at 1.43 FPE/CI.... With the gap increased to 5 turns, the velocity averaged 960 fps (37.1 FPE) at 1.64 FPE/CI.... and at 6 turns the average was 844 fps (28.6 FPE) at 1.95 FPE/CI.... Remember, this is at only 1150 psi.... The ES over the 10 shots was around 14-15 fps for most strings, although for the one at 4T out it was only 7 fps (0.7%).... Typically SSGs have a narrower ES when the preload is set so that the gap is small (0.020-0.060"), but I didn't bother reducing the preload before shooting these strings, so the gap at 6T out was actually over 1/4".... (over 1/3 of the hammer travel wasted)....

I then filled the gun to 2900 psi (my Great White needs filling), and shot an entire string with the gun adjusted for 38 FPE (an average velocity of 972 fps with the 181 gr. JSBs).... I stopped when the first shot dropped below 950 fps, which occurred at shot 45.... Yep, that's a total of over 1700 FPE on a single fill.... Here is the string....

Image

The ES wasn't great, about 2% with unsorted pellets and the large gap in the SSG.... You can see what happens to the pressure curve at the regulator setpoint of 1150 psi, the slope decreases because both tubes are dropping in pressure below that.... I got 35 shots from 2900 psi to the setpoint, another 5 below that down to 1000 psi.... and another 5 shots before the declining velocity opened the ES up to 4%.... The overall efficiency over the 45 shots was 1.44 FPE/CI, down a bit from the results above at 37 FPE.... so I appear to be right in that area where a slight change in gap and velocity makes a big difference in efficiency.... If I were really interested in tuning for these pellets, I would use less preload on the hammer spring and reduce the gap in the SSG to make the gun easier to cock.... I would expect that to narrow the ES and increase the efficiency as well....

This completes my testing of the regulator, now it's time to change out the SSG for a conventional preloaded spring (temporarily) so that I can crank the power up with heavier bullets and see just what this gun is really capable of....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Dec 24, 2016 5:26 pm 
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Time to get down to business tuning this gun the way I wanted it in the first place.... The SSG using the QB spring did not have quite enough power, so I replaced it with a conventional RVA using the same spring but with preload.... In addition, I added a lightweight sliding spring guide as a valve lift indicator, so that I could make direct measurements of the valve lift at various preload settings.... Here is the SSG (lower) and the Lift Measuring Rod for comparison....

Image

The same spring (from a QB) is used in both, so you can see how much preload I have in the SSG.... Conversely, you can see that with the preloaded setup, the spring will still be pushing the valve open throughout the entire shot cycle.... The Lift Measuring Rod is just a piece of 3/16" K&S aluminum tubing with a short flathead 8-32 screw in the end.... the head of the screw ends up captured between the spring and the hammer, so the tubing slides with the hammer.... There is a #008 O-ring on the end, which you push up against the RVA adjusting screw, then cock and fire the gun.... Since the tube travels with the hammer, the O-ring slides back along the tube the same distance the valve opens.... so the distance between the RVA screw and the O-ring is the same as the valve lift....

The regulator pressure was still sitting at 2000 psi, within as close as I could measure it, so the regulator seems to have settled down nicely and is now showing no signs of creep overnight.... When it was brand new, it was gaining about 100 psi overnight, and it is not unusual to see a short "break-in" period like this.... I filled the lower reservoir to 3000 psi, cranked the preload to maximum (coil bind), loaded the magazine with the new 34 gr. JSB Beasts, and fired 3 shots across the Chrony.... The velocities were 1006, 997, and 997 fps, and it used 1000 psi for the three 75 FPE shots.... Incidently, 75 FPE is exactly what my Spreadsheet predicted for my "lofty goal" with a 24" barrel at 2000 psi.... The barrel on this gun (although I ordered a 25") is 28" long, so that is 100% consistent with my expectations.... to fall short of the spreadsheet prediction by a small amount.... I measured the valve lift, and the O-ring gap was 0.200", which is all the travel the valve stem has before being driven flush with the back of the valve, so I had all the hammer strike I can possibly use (and more than I need).... I turned the RVA out 1 turn, shot another 3 shots, recorded the velocity, pressure drop for 3 shots, and valve lift, and continued doing that until the velocity dropped below 600 fps.... Here are the results....

Image

Image

There is a LOT of useful information in those two charts.... First of all, the velocity plateau, which is at 997 fps, starts when the preload is backed out 6 turns (1/4") from coil bind, and in fact there is no real drop in velocity for the next couple of turns.... At 6 turns out, the pressure dropped 580 psi for 3 shots averaging 994 fps.... but at 8 turns out, the pressure dropped only 400 psi for 3 shots averaging 983 fps.... At 9 turns out, the pressure only dropped 320 psi for 3 shots averaging 963 fps.... In that 3 turns of adjustment, I lost 3% in velocity and used 45% less air.... and the efficiency increased from 0.74 FPE/CI to 1.25 FPE/CI.... Compared to maximum preload, when the hammer was hitting the back of the valve, it is only using 1/3rd of the air.... So 9 turns out is clearly the "knee" of the curve, with the downslope starting at 10 turns out.... You will also notice that until the preload was backed off 2 turns from coil bound, the lift stayed constant at 0.20" because that was the maximum the valve could physically open.... At 6 turns out, where the velocity just starts to drop, the lift is down to 0.14", and at 9 turns out, at the knee of the curve, it is just 0.10".... It is that decrease in lift, and its associated decrease in dwell, that decreases the amount of air released by the valve.... Since the throat of the valve is 0.266", driving the valve more than half that distance open gains nothing in power, it just wastes air.... I have seen this many times before, and now believe it to be a good rule of thumb for how much you need to allow the valve to open.... If it can physically open more than half the throat diameter, that's all you need to allow for.... That means that shortening the valve stem can allow for more useful hammer stroke, which can then reduce the cocking effort.... I may in fact drill a recess in the front of my hammer to allow another 0.050" of hammer stroke.... That should have NO impact on the maximum power, I should still be able to reach the plateau, even with the 34 gr. pellets....

I haven't yet shot a full string with the 34 gr., but based on these tests I should be able to get one 10-shot magazine at 960 fps (70 FPE) by the time the pressure drops to the 2000 psi setpoint.... and that was my goal.... In fact, when I started, I planned on using a PRod magazine, and they are only 8 shots.... but at that time I was unsure if I could get enough power at 2000 psi, and thought I might have to use 2200 for my setpoint.... I did fire a few shots with my 30 gr. BBT, and at 9 turns out the velocity was 1023 fps, dropping to right around 1000 fps at 10 turns out, so logically I should be able to get more than 1 full mag. with the BBTs.... One other thing I should mention, there is a BIG decrease in the report when you hit the knee of the curve, which is to be expected....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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