Canadian Airgun Forum

Here are the receivers with everything now done except to machine the 20-25 MOA slope in the scope mounts and cut the dovetails in them....



On the lower front corner you can see the semi-circular recess milled to act as a clamp for the plastic pipe forestock.... It pinches the pipe between the bottom of the receiver and the main air tube, mounting it solidly at the back in the lowest possible position so that it doesn't rattle around, and clears the barrel.... The velocity adjusting screws are installed in the back, in line with the lower bolt slot.... The 8-32 SHCS pushes on a 1.5" long steel pin that can prevent the bolt handle from retracting fully in the slot.... I have about 10 turns of adjustment, the back receiver has the adjuster fully retracted (maximum velocity) and the one in front has the adjuster set to minimum velocity.... I labelled the steel pin which is sticking out into the lower bolt slot, which holds the bolt forward so that the nose obstructs the barrel port, reducing airflow (to almost zero when fully closed as shown).... You can't see it in these photos, but there is a vertical hole coming up from the bottom, in line with the bottom of the adjusting screw.... It is tapped for a 6-32 setscrew which presses on a 1/4" long piece of thin Teflon rod which acts as a brake to prevent the velocity adjusting screw from moving by itself....

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!

I got to work on the barrels today.... The first order of business was to machine the breech end to 1/2" OD for 1" of length so that it will fit into the receiver.... In addition, I had to machine down the OD of the carbon fibre tube slightly to fit inside the 25/32" forward section which is drilled to a depth of 2.5".... I did that with the end of the tube running on a live center in the tailstock of the lathe to insure concentricity between the ID and OD, and it worked out great.... Both the CF sleeve and the barrel slide perfectly into the receiver and can be rotated individually, showing they are concentric with each other and the holes in the receiver are as well.... This was a bit of a nervous time, as any inaccuracy there would have been hard to correct.... At the muzzle end I turned the barrel down to 1/2" as well and threaded it 1/2"-20 NF so that it can accept either a Hatsan Air Stripper (as a backup) or my intended Harmonic Tuner, which I have yet to make.... Here is a photo of the barrel ends, breech on top, muzzle below....



and here is a photo of them with the CF sleeve in place (but not bonded yet)....



You can see where I had to skin down the outside of the CF tube to fit the 25/32" hole in the receiver, just a few thou was all that was required.... The next job will be to cut the chambers in the barrels before bonding on the CF sleeves.... I think the reamer I made for my .257 Monocoque will work, but I will have to make a new chamber reamer for the 6 mm.... I received some samples from Nick at Nielsen Specialty Ammo in the mail today (perfect timing, thanks Nick), as I would like to make sure the chamber in the .257 will accept as many different bullets as possible.... Here is a photo of the selection of .257 bullets I now have to try....



Left to Right they are.... My 98 gr. BBT HP, the 91 gr. Noble from Nick and his 85 gr. rebated boattail HP, an 88 gr. RCBS 82301, an 82 gr. NOE 260-80 FN, and a 73 gr. Lyman 257420.... I can also cast HP versions of the 82301 and 257420, so I will have lots of bullets to choose from.... I don't expect the 98 gr. BBT (or the FN version of it) to work in the 10" twist of the TJs barrel I have.... so if the chamber has to be too short to fit all the other bullets for it to chamber, so be it.... but just looking at the position of the ogives in the above photo, I think I can cut a chamber that will work with all of them.... If anything, the bullet with the Ogive starting the furthest forward is Nick's swaged HPBT.... Here are the 6mm Bullets.... the TJs barrel I have is also 10" twist....



Left to Right they are.... 58 gr. Bowman HP from Arsenal, 59 gr. NOE 245-64 HP and 69 gr. NOE 245-74 HP.... I can also cast FN versions of all three bullets.... The weights of the FN versions are 61 gr., 63 gr. and 73 gr. respectively.... The 63 gr. NOE is a shortened, FB version of the 73 gr. beside it, with the GC shank removed.... I also have a mould for a 65 gr. shortened version of the NOE 260-80, done the same way, but that will be too light for the power of this .257 cal (I hope)....

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!

I worked on making the Harmonic Tuners today.... I got two of the brass weights made, and one of the mounts that screws onto the muzzle.... Here is what it looks like when assembled....



The threads are 15/16"-28.... I like 28 TPI for this job because 10 deg. of rotation is 0.001" of movement (1 "hour" on a clock face is 0.003", 1 turn is 0.036").... The brass weight is made from a piece of 1.5" bar stock 1" long, the setscrew presses on a short piece of Teflon rod which acts as a brake to prevent the weight from moving by itself.... The mount is made from a piece of 1" CRS.... There is a small collar of that diameter at the front, with a 3/16" hole drilled though it to allow it to be tightened onto the muzzle with a short piece of 3/16" bar stock.... The remainder is threaded, the 2" of threads giving over 1" of adjustment for the weight.... The center portion is threaded inside 1/2"-20 NF to thread onto the barrel, and the back is counterbored 0.80" ID for 1" of length to fit over the CF sleeve.... The front is drilled out 3/4" ID, it only projects 1/2" past the muzzle to allow the HPA from the shot to escape quickly without affecting the bullet.... and it also serves to protect the crown which is a simple 90 deg. angle....

The mount weighs a couple of ounces, and the movable brass weight weighs just over 5 oz. at the present time, although I may put chamfers on the corners for appearance after initial testing.... I'm really looking forward to trying this system, I know it is tremendously successful in rimfire benchrest, where it can drastically affect the group size....

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!

Amazing work Bob! It'll be interesting how the movable weight effects accuracy. I found moving the barrel band around made a huge difference on the Snowpeak guns I built.

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Website: https://airgunarcheryfun.ca/

Here are the completed harmonic barrel tuners.... The muzzle of the barrel is about 3/8" inside the front of the mount, about where the outside threads start....



The scale is like a clock face, with the quarters having longer index marks.... with 12 o'clock being where the setscrew is.... Each mark equals 0.003" of movement on the tuning weight.... By starting with the weight against the shoulder at the front, you can record the position using "hours" for the turns and "minutes" for the index marks, so 9-1/3 turns I would record as 9:20.... and 15-3/4 turns as 15:45 etc.etc.... I'm really pleased with the way they turned out....

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!

I cut the chamber in the .257 barrel today, using the reamer I made for my Monocoque....



Here are all the bullets that will fit.... They were all chambered to a depth of 0.60" from the end of the barrel, which will put the base just ahead of the front of the barrel port.... All bullets were sized to 0.257" before testing how they chambered.... When the chamber is too short, you sure know it, as you have to push hard enough to mark up the base, and it's pretty obvious when you get the length right....



I enhanced the contrast as much as possible so that you can see the rifling marks, but they are still hard to see on all except the longest two BBTs (112 gr. FN and 98 gr. HP), where they are clear on the back of the head.... The shortest bullet is the Lyman 257420 73 gr. and it barely touches the leade.... If you push it in by hand, you can only feel resistance for about the last 1/16", and basically cannot see any marks, even with a loupe, unless you push it in another 1/16", where you feel significant resistance.... I don't expect the two longest bullets to work in the 10" twist in this barrel.... but since I can chamber them I will be able to test that and prove or disprove the validity of the Kolbe Twist Calculator numbers for them.... Many of my BBTs seem to be stable in a slower twist than it gives, so there is a chance that the 98 gr. HP may work.... providing I have enough power to push it....

The other four bullets all slid in between 0.50-0.54" and then took a bit of a push (not much, mind you) to seat them to 0.60".... If you look carefully you can see shallow marks from the tapered leade, which they are sitting firmly against when chambered.... Those 4 bullets, from L to R, are the 91 gr. Noble, the 85 gr. NSA BTHP, the 88 gr. RCBS 82301, and the 82 gr. NOE 260-80 FN.... If I find one particular bullet shoots the best and want to play with different seating depths, I can do that by changing the length of the bolt nose....

Next step is to make the bolt, cut the O-ring groove and polish the chamber behind the barrel port.... then cut the CF sleeve to final length and glue it on.... and then machine the barrel port.... I was very pleased with the way the 3-flute reamer worked, so I am going to copy that design when I make the one for the 6mm barrel.... just smaller diameters for the pilot and chamber of course....

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!

I made the 6mm reamer this afternoon.... still not hardened and tempered but it turned out dimensionally accurate....



It is made from O1 Drill Rod.... The next step is to heat it to cherry red and quench it in oil to harden it.... Then I will polish it, hone the cutting edge again, and then temper it in the oven.... tomorrow's jobs....

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!

Amazing work all around! Thanks again for sharing the progress as it goes along. Do you heat it cherry red with just a blow torch or do you have some kind of blacksmith oven/forge with bellows to get it super hot?

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Website: https://airgunarcheryfun.ca/

I use an oxy-acetylene torch, taking care to have a large, rich flame (blue but bordering on yellow, with a large inner cone).... This helps avoid burning off the carbon in the outer layer of the steel.... Coating the part with soap (ivory bar, rubbed on) before heating helps prevent some of the black scale from forming when you quench.... Technically you only need to heat to the point where the metal looses the ability to be attracted by a magnet before quenching.... but cherry red is what I use.... I quench in vegetable oil....

The resulting reamer is glass hard, and needs to be tempered in an oven to make it tougher.... You need to have a clean polished surface so that you can assess the colour of the oxide layer forming during tempering.... I like to see a "dark straw" (looks brown to me).... You first get a yellow, that darkens, goes through brown to purple and then blue.... Yellow is very hard but brittle (scribers), blue is very tough but not too hard (springs).... Dark straw to brown is what I like for reamers.... which is 250-260*C.... I set my wifes oven to 465*F and it takes about a half hour to get to the right 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!

Thanks for the great tips!

Sent from my LG-H812 using Tapatalk

_________________
Website: https://airgunarcheryfun.ca/

Here is what the finished reamer looks like....



It was hardened, polished, and them tempered for 30 min. at 465*F, raising the temperature to 480*F for the last 5 minutes because it was a little too pale a straw colour.... The result is a nice brown, the way I like my reamers....

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!

Nice!

Sent from my LG-H812 using Tapatalk

_________________
Website: https://airgunarcheryfun.ca/

It's always a nervous time when you first use a new chamber reamer.... They seem to get smaller through the polishing, hardening and repolishing, and I'l always wondering if it will cut the chamber to the right diameter.... When I set up to cut the chamber in my 6mm barrel today and starting advancing the reamer, it went so easy I thought "carp, it's too small".... I cut the leade into the barrel about 1/4", and then pulled it out.... To my surprise, and delight, I found that it cut better than any reamer I had ever made before, and the little channel between the flutes that I had filled with oil had a nice pile of shavings sitting in it....



Usually you can "feel" quite a bit of resistance on the handwheel on the tailstock as you feed the reamer in, the barrel gets warm, and the shavings are not much more than dust size.... Not so with this reamer, the shavings were like little needles, about 1/16" long and 0.005" in diameter or so.... I could actually feel the "bump-bump-bump" as each flute hit the rifling lands and slowly carved them away.... I don't know why this one is so much better.... but I hope they all come out like this from now on.... It may be that I honed it just right.... I know I will try the same honing technique on another reamer the next time, to see if that was the difference.... I sure hope so, this one cut a beautiful chamber in short order.... Here are the three 6mm bullets I used to set the length....



Left to Right are the 63 gr. NOE 245-64 FN.... the 61 gr. Bowman by Arsenal.... and the 73 gr. NOE 245-74 FN.... The 63 gr. is a shortened version of the 73 gr., with the gas check shank missing.... These two bullets are "bore riders", and you can see the shiny spots on the nose of the 73 gr. where it rubbed along the lands.... The front driving band is engraved to about half the rifling depth, as it is sitting in about the middle of the leade.... There are very slight marks on the rear band from the back of the leade, and about the same on the back band of the Bowman (which is a copy of the Lyman 257420, scaled down to 6mm).... The middle band of the Bowman is engraved about half depth, and the very front of the front band is just about full rifling depth, which is what I aim for.... The 63 gr. barely touches the leade with the front band, but if you push slowly on it, you can feel that it is seated firmly against it, but just enough to leave tiny marks.... There are some tiny polished spots on the nose, just at the back of the ogive, where it is just sitting on the lands.... I'm very pleased with the way this chamber came out.... In terms of size, a bullet sized to 0.243" slides in easily.... but one sized to 0.244" requires a bit of a push.... so the chamber size is perfect.... This reamer is a KEEPER !!!

This afternoon I set up the receivers in my milling attachment in the lathe, and adjusted it so that it cut a 20 MOA angle into the top of the Dovetails.... That works out to only about 1mm (0.040") less height at the front of the dovetail than at the rear.... but should put the POI at about optical center of the scope at 100 yards.... I then machined the dovetails into the sides of the raised portions on the receivers.... I took a bunch of photos of the two receivers with the dovetails, and had trouble with reflections hiding the angle of the dovetails.... but you can just about see that in the photo below (with a little imagination)....



If you look closely, you will see that at the front of the dovetail, the bottom of the cutter ran along the top edge of the bevel on the corners of the receiver.... but at the back of the dovetail the cutter left a ridge 1mm above the top of the bevel.... It's hard to believe that is all the elevation angle required of the barrel, relative to the scope, to put you on target at 100 yards.... but 0.040" in 6" works out to 24" at 100 yards (0.040 x 100 x 3 x 12/6).... When you mount the scope you can barely see the angle, if you didn't know it was there you would never notice it....

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!

Wonderful work! Very inspiring! To have everything turn out so well is a testament to careful planning and skill. Congrats on how its all coming together!

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_________________
Website: https://airgunarcheryfun.ca/

Over the last 3 days I machined the O-ring groove in the breech of both barrels, and cut the CF sleeve to length and glued it onto the barrel liner with Loctite 638 (green).... After curing 24 hours, I gave it a post-cure in my wife's oven at 175*F for 3 hours.... This greatly enhances the strength of the bond.... Today I laid out and machined the barrel ports, and then installed each barrel in its receiver with a couple of setscrews (just tightened a bit against the CF sleeve), making sure the flat on the barrel port was perfectly centered in the hole in the receiver for the transfer port.... I made a drill jig from a 20mm long x M5 SHCS by drilling a 1/8" hole through it in the lathe.... and then inserted it in each of the holes in turn and drilled through the carbon fibre until I touched the steel of the barrel with the 1/8" drill bit.... I then mounted the barrel in my milling attachment in the lathe, centering off each 1/8" pilot hole, and enlarged the hole to clear the M5 setscrews with a #8 drill.... I drilled deep enough to leave a shallow pocket in the steel liner for each screw.... Here is the way that works....



The piece of tape on the drill bit was just a visual indicator to let me know when I would hit the steel.... The drilled out M5 SHCS worked perfectly as a drill guide, it is a great way to mark setscrew pockets accurately in a barrel.... I deburred the barrel ports and faired the 0.260" round transfer port seat ID into the oblong barrel port which had been machined with a 3/16" end mill.... The port in the 6 mm ended up at 0.194" wide by 0.294" long and the one in the .257 is 0.205" wide by 0.305" long.... which gives me full bore-area porting in both barrels.... Here is a photo of one of the finished barrels installed in the receiver....



The next job is to complete the bolts.... I already have them turned down to diameter, but have yet to install the bolt handles and cut
them to length at both ends.... The barrels also need lapping inside with JB's Bore Paste and polishing with Bore Brite.... I'm getting pretty close to being able to take the first shots....

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!