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PostPosted: Sat Dec 24, 2016 8:18 pm 
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Location: Coalmont BC
I milled a 3/16" diameter recess in the front of the hammer that is 0.050" deep to increase the hammer travel to 0.75".... Without changing the preload I gained about 20 fps at the 10T out position.... This is because the cocked force is the same but the uncocked force is less, dropping the average spring force slightly while increasing the travel distance.... This slightly increases the hammer strike without any increase in cocking force.... I shot a 10 shot string at that setting, and it had not dropped below the setpoint, proving the gun is capable of doing that with the 34 gr. JSB Beasts in the mid 900s on a 3000 psi fill....

I then shot a few shots with my 29.6 gr. BBT FN bullets at each preload from 10 to 12 turns out.... It was nearly 1000 fps at 10 turns, and just under 900 fps at 12 turns.... so that determined that 11 to 11.5 turns will be the likely setting for the FN bullets in the mid 900s.... It was about 50 fps faster with the 27.4 gr. HPs, so 12 turns out will be quite close for those.... I also shot some short strings with bullets sized at different diameters at 11 1/4 turns out, and got the following average velocities....

0.216" FN .... 972 fps
0.217" FN .... 963 fps
0.218" FN .... 956 fps
0.219" FN .... 956 fps
0.217" HP .... 1007 fps

I was curious what the relationship would be between diameter and velocity, and as expected the smaller bullets shot faster, because of less resistance inside the barrel.... I wondered about why the "as cast" bullets (they are the 0.219") weren't slower, and then I remembered that the chamber is 0.218", and the bullets were noticeably harder to load than the others.... so it was resizing them to 0.218" before they were shot, hence the reason the velocity stayed the same.... The total pressure drop for 10 shots was around 950 psi, so the pressure stayed above the setpoint for all 10 shots, in fact I would expect the 11th shot to not lose any velocity.... not that it matters, because it is a 10 shot magazine....

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 8:36 pm 
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Location: 1/2 Way From Ottawa and Montreal,
Very nice great velocity and shot count great job and looks great similar to my build the skeleton.

now my questions are. how well does it group at 50 meters and what size game can it take down in 1 hit?

I really enjoy all your post Bob

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PostPosted: Sat Dec 24, 2016 10:01 pm 
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Accuracy testing will have to wait until late Spring.... I would think anything up to Coyote, but for that a fusebox shot only....

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: Mon Dec 26, 2016 5:29 pm 
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I installed the shroud today, and a scope and bipod.... It weighs 8 lbs. 10 oz. complete, or 8 lbs. even without the Bipod.... Without the scope and rings it is about 6 lbs. 12 oz....

Image

I played around with the preload to find a setting that could work for both weights of BBTs and the 34 gr. JSB Beasts.... The RVA ended up at 11.25 turns out from coil bind.... and the gun is quite easy to cock like that.... I then shot some 10-shot strings, refilling to 3000 psi each time.... At the end of the strings it was pretty much right on the 2000 psi setpoint.... so I can shoot one magazine on a fill.... Here is what they look like....

Image

The 34 gr. JSB Beasts averaged 874 fps (57.9 FPE) at an efficiency of 1.35 FPE/CI.... The 29.6 gr. BBT solids averaged 944 fps (58.6 FPE) at 1.24 FPE/CI.... and the 27.4 gr. BBT HPs averaged 988 fps (59.4 FPE) at 1.21 FPE/CI.... This was using BBTs sized to 0.217".... The ES on the Beasts was just 6 fps (0.7%), and with the BBTs is was just under 2%.... That should prove close enough for shooting out to 100 yards....

I then took the opportunity to see what adjusting the barrel tension does to the group size.... Without the shroud, the 28" barrel was pretty whippy.... It shot OK inside my shop, but the distance is only 20 ft.... Still, I can usually tell if the gun is a shooter or hopeless just during my Chrony sessions at that distance, if I pay attention to aiming.... The JSB pellets were pretty much all 5 touching, but the BBTs ranged from that to a loose 5-shot group you could just cover with a dime.... I installed the shroud, but with no tension on the Bellevilles, just enough to keep the tension adjusting nut from falling off the muzzle.... This did, however, drastically raise the POI, because I had indexed the barrel to the bottom, and it had a noticeable curve to it.... Once I rezeroed the scope, and using the 34 gr. JSB Beasts, I shot a series of 5-shot groups, tightening the nut on the Bellevilles 1/4 turn at a time.... I am using a stack of 5 Bellevilles, and they have a rate of 750 lbs. per 0.010" (singly), so that means each 1/4 turn increased the barrel tension by about 200 lbs.... I stopped at 1.5 turns, which would be about 1200 lbs. of tension in the barrel.... In theory I can go another 1/4 turn without driving the Bellevilles flat, but I don't like to do that, you can ruin them by causing them to take a "set".... I disassembled the stack after tensioning to 1200 lbs., and they had only collapsed less than 0.001" each, so I will use that 1.5 turns as my limit.... Here are the group sizes as I increased the tension with the 34 gr. Beasts....

0 lbs. tension = 0.30"
200 lbs. = 0.44"
400 lbs. = 0.22"
600 lbs. = 0.36"
800 lbs. = 0.19"
1000 lbs. = 0.17"
1200 lbs. = 0.28"

I then repeated the process with the 29.6 gr. BBT FN, sized to 0.217"....

400 lbs. tension = 0.38"
600 lbs. = 0.53"
800 lbs. = 0.48"
1000 lbs. = 0.59"
1200 lbs. = 0.15"

I then tried the 27.4 gr. BBT HP's, also sized to 0.217"....

800 lbs. = 0.45"
1000 lbs. = 0.21"
1200 lbs. = 0.34"

and then at that 1000 lbs. setting I tried other diameters of the HPs....

0.216" = 0.32"
0.217" = 0.21"
0.218" = 0.24"
0219" = 0.25"

I then reduced the tension to 1 turn (800 lbs.) and tried the HPs again....

0.216" = 0.22"
0.217" = 0.45'
0.218" = 0.15"

What I had been told was that once you reached a certain barrel tension, tightening past that point would not decrease the group size.... What I found was that low tensions did not work well, and that I do indeed need about a turn on the Bellevilles (about 800 lbs. of tension) as a minimum.... However, past that minimum, each bullet appears to have it's own optimum tension setting (sweet spot).... and that can change when you change the bullet diameter.... It likely also changes with the velocity.... In fact, anything that changes the dynamic vibrations of the barrel will likely move the sweet spot a bit.... The good news is, that the group size is dramatically reduced by using the tensioned barrel.... I would say that is a 100% success....

Incidently, when I started testing the tension adjustment I found that the POI on the target was walking around in a 6" circle, even at just 20 ft., as I changed the tension.... Since I had drilled only a 1/4" hole in the barrel extension that holds the Bellevilles, I suspected that the pellets were clipping the inside of it.... I removed it and couldn't see any marks inside, but I drilled it out to 9/32" (to provide 1/32" clearance for the pellet) and this went away completely.... There was a slight POI change with tension, as you would expect, but we're talking 1/2" instead of over 10 times that much....

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: Tue Dec 27, 2016 9:50 pm 
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Location: Coalmont BC
I made a few small changes to the gun today.... I removed the top portion of the rear triple band because it interfered with the scope position.... It now only clamps the two reservoirs together.... The forward band remains the same, with an O-ring supporting the shroud, so that it can move independently of the reservoirs for expansion, but is located to prevent damage if you drop the gun or fall on it.... I call this arrangement "semi-floated".... I added an internal support, just a simple collar that is setscrewed to the barrel, with an O-ring in a groove that is in firm contact with the inside of the shroud, flush with the front of the band that supports the shroud.... That places it 3/7ths of the distance from the receiver to the muzzle, to dampen any harmonics between the tensioned barrel and the shroud.... I also machined twelve marks on the tension adjusting nut, to make a Vernier so that it is easy to ascertain the position of it during tuning the tension.... Every 3rd mark is slightly longer (3, 6, and 9 o'clock), and the 12 o'clock mark is the longest, and marked with black.... There is a corresponding mark on the top of the flange on the CF shroud that doesn't rotate as a reference mark....

Image

It is the one that was vertical when the nut just touched the Belleville washers, and when tightened one turn puts nearly 800 lbs. of tension in the barrel.... I can tighten at least another half turn from there, and I can record the position as "3 o'clock", or "4:30", or "5:20".... which will make it easy to return to the setting which worked the best.... Each "hour" of rotation is about 65 lbs. of barrel tension.... I haven't yet tested the gun with the intermediate barrel support, and the Motel is booked until after New Years, so it may be a few days before I get the chance.... and even then it will only be at close range inside my shop.... I am hoping the intermediate support will even out the differences between pellets, and allow one tension setting to work for all.... I guess we'll see what happens....

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: Thu Dec 29, 2016 5:32 pm 
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Joined: Sat Nov 03, 2007 4:19 pm
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Location: Coalmont BC
I burned through another tin of 34.1 gr. JSB Beast pellets today (actually more than a tin), playing with the tension adjustment on the barrel.... I found out that a "1 hour" change (about 65 lbs.) to the tension makes a significant difference to the group size.... but that virtually all the groups are better than previously, since I installed the intermediate support on the barrel.... Having a support between the barrel and shroud at 3/7ths of the distance from receiver to muzzle really settled down the variation in group size as you change the tension, bullet, or velocity....

I increased the velocity with the Beasts to 960 fps (70 FPE), and found that there was a sweet spot just past 1 turn of tension.... Using a 24 hr. clock, starting from zero tension, 1400 hrs. (2 hrs. past 1 turn) gave me the best groups.... Here is an example.... Yes, that is a 34 gr. JSB Beast .22 cal pellet sitting in the hole from a 5-shot group....

Image

About half the 5-shot groups at that setting met the "Feinwerkbau Test".... Although I only have 20 ft. available, not the 10M that FWB uses.... I find that when a gun shoots like this inside, if there is a problem at long range, is tends to be the pellet/bullet, not the gun.... At this velocity, I am running right on the knee of the curve at the 2000 psi setpoint with the Beast, it uses 1200 psi for 10 shots, which works out to 1.13 FPE/CI.... I think that is pretty good for a .22 cal at 70 FPE.... With a 3000 psi fill, the last shot (taken below the setpoint) loses about 100 fps, but by filling to 3200 (the gun is safe to at least 3500 psi) the gun is sitting right at the 2000 psi setpoint at the last shot, and the ES is hovering right at 1% (8-10 fps) over the 10 shots....

This is pretty much the kind of tune I was looking for, so I think I'm done with the development of this gun until I can get outside in the Spring to test at longer ranges.... I can chalk this up to another very successful project.... with many thanks to Lloyd Sikes for supplying his new Regulated Disco Double Kit so that I could put it through its paces.... I would highly recommend it for anyone modding a Discovery.... It is capable of a ton of shots at lower pressures, and lots of power when you crank the pressure up.... The external adjustment is easy to use, and covers a wider range than I needed (I used 900-2200 psi during this project).... It can be used with a stock Disco, or one that is highly modified like this one.... I don't see how you can go wrong with it.... Congratulations, Lloyd, on another fine product from the AirGunLab....

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 Jan 04, 2017 6:01 pm 
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Location: Coalmont BC
I wanted to find out what affect the Velocity Adjusting Screw on the back of the receiver had, and document it, so I did some testing today.... I tried three different weights at each of the 10 settings (1 turn apart) on the 8-32 adjusting screw by shooting a few shots, taking the average velocity, and plotting the results.... Here is that data....

Image

The nose of the bolt doesn't quite block the barrel port completely, because the front end of the port is rounded to streamline the flow into the barrel.... and when you first start obstructing the port, the velocity doesn't start to drop until you turn the screw in a couple of turns, even though you can see the nose of the bolt through the back of the barrel and transfer port.... I presume this is because there is a bit of wasted volume in the back corner of the chamber, causing a bit of pressure loss when the bolt is fully retracted, which counterbalances the obstruction of the hole when you first start moving the bolt forward.... The black line represents my best estimate of the percentage of barrel port available at each turn of the adjusting screw....

Note that at 2000 psi, the 18 gr. JSB Heavies are Supersonic, hitting nearly 1200 fps.... in fact they don't drop below Mach 1 until the port is about 50% obscured.... I was interested in finding a setting in the mid 900s with each weight, so that I could run a string with each pellet/bullet.... It turns out that with the 18 gr. JSB Heavies I only needed the adjuster open 2 turns, and with the BBTs 4 turns, compared to wide open for the 34 gr. JSB Beasts.... I then used those settings and shot a string starting at 3000 psi, until the velocity dropped off.... Those strings are shown below....

Image

You will note that with the 34 gr. Beasts I get 10 shots, averaging 67 FPE, before the velocity starts to drop off.... With the 30 gr. BBTs, I get 11 at 57 FPE.... and with the 18 gr. JSB Heavies I get 15 shots at 36 FPE.... The efficiency is slightly lower with the BBTs, 1.13 FPE/CI compared to 1.18 with the Beasts.... and even lower with the 18 gr. heavies, down to 1.00 FPE/CI.... This is in sharp contrast to what happens to the efficiency if you back off on the hammer spring preload to reduce the power, instead of choking up the ports.... It makes perfect sense, because choking the port has little effect on how much air the valve releases (other than a bit of increased backpressure), because you aren't really changing the dwell, you are just forcing the air to flow through a smaller port, which is less efficient.... This means that for a quick adjustment in velocity to go with an ammunition change, the Velocity Adjusting Screw is great.... but if you are after increased shot count there are better methods.... Reducing the hammer strike will give you great efficiency, but the velocity will bump up below the setpoint.... A better way is to reduce the regulator setpoint AND the hammer strike, as I showed with the 18 gr. JSBs much earlier in this thread.... I have found previously, however, that a combination of all 3 methods produces the best shot strings with lighter pellets.... In my .25 cal Disco Double, with the basic tune set to shoot 50 gr. bullets at 100 FPE.... the best strings with JSB Kings were achieved with a lower setpoint, less hammer strike, and a slightly restricted barrel port.... It's nice to have the option of that added tuning element when you want to go plinking....

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: Wed Jan 04, 2017 6:40 pm 
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The second half of today's testing was penetration and expansion testing of the different pellets and my new Bob's Boattails, both the 29.6 gr. FN and the 27.4 gr. HP.... I used the same settings of the velocity adjuster as for the strings above, 2T out for the 18 gr. JSB Heavies, 4T out for the BBTs, and 9T out (wide open) for the 34 gr JSB Beasts.... The test medium is my standard "Melt-and-Pour" soap, cast into blocks big enough to stop the bullet.... Here is a photo of the block with the four rounds inside it....

Image

The BBT Hollowpoint is entering from the left (at 57 FPE).... From the right, top to bottom, are the 18 gr. JSB Heavy (at 36 FPE), the 34 gr. JSB Beast (at 67 FPE) and the 30 gr. BBT FN Solid (at 57 FPE).... Those FPE levels are the result of wanting all the bullets to be in the mid 900s fps range when they hit the block of soap.... The 34 gr. Beast had by far the greatest penetration, at 6.5".... The 30 gr. BBT and the 18 gr. Heavy were nearly identical, at 4.2" and 4.1" respectively.... while the 27 gr. BBT HP exploded violently and dumped its energy by creating a large cavity before stopping only 2.4" into the soap.... The volume of the wound channel in the block is roughly proportional to the FPE.... I then cut the block apart to photograph the wound cavities with the bullets still in place.... Here is the photo of the 18 gr. JSB and the 30 gr. BBT FN....

Image

Now you can see why the BBT stopped in about the same distance as the 18 gr. JSB.... even though it had way more FPE.... The pellet hardly changed at all, which the large Meplat of the BBT expanded to well over bore-size, while leaving a much larger diameter wound channel than the pellet.... kind of the difference between an ice-pick and a sledge-hammer.... Next is the photo of the 34 gr. Beast and the BBT HP....

Image

The block cracked behind the JSB Beast, so I didn't get to photograph it, but the wound channel was long and thin.... and you can see the pellet was hardly changed at all by the 67 FPE impact.... Not so the 27 gr. BBT Hollowpoint.... It literally blew apart after entering only about 3/4" into the soap, leaving three large fragments of the nose (and 1 small one) behind as the base (and 1 more fragment) continued penetrating.... Below is a photo of the bullets and pellets after recovery.... BBTs on the left, pellets on the right....

Image

As you can see, round nosed JSB Pellets punch through and penetrate with very little change in shape.... Both pellets showed a very slight flattening in the center of the nose, and you can see how the skirts have obturated (blown out) from the pressure inside the skirt.... The Meplat on the BBT FN solid nearly doubled in diameter, showing how effective the large (70%) Meplat is in providing energy transfer to the target while limiting penetration.... The Hollowpoint BBT, however, is in another class entirely.... The nose section blew apart, creating a wound cavity in the soap nearly 3 calibers wide, while the rear portion of the bullet mushroomed completely and continued to penetrate, although less than 60% of the distance penetrated by the solid.... I would suspect that bullet to be devastating on Varmints.... and look forward to trying it out in the Spring....

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: Thu Jan 05, 2017 8:17 pm 
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Location: Coalmont BC
I made one additional test today, I reinstalled the SSG.... I had not tried it since I increased the hammer travel to 0.75" and adjusted the setpoint to 2000 psi.... There was no problem getting either weight of BBT into the mid 900s with a decent gap, and I could just barely push the 34 gr. Beasts at 950 fps (68 FPE) with the gap adjusted to zero (but no preload).... There is still room to increase the hammer travel slightly, which would give me room to create a gap and still shoot the Beasts at 70 FPE.... but with the stunning performance of the BBT Hollowpoints in my expansion tests, and assuming I can get them to shoot accurately, I think I will set the gun up for those.... With the gap increased to 0.10" (2.5 turns out), the velocity with the 27.4 gr. HPs was 960 fps, and I shot a 10 shots string with an ES of just 10 fps (1%) using just 740 psi of air.... and a LOT quieter.... That works out to 1.45 FPE/CI, a 28% increase in efficiency compared to the same spring with preload at the same FPE.... The gun is a bit harder to cock, which could be fixed easily by using a longer, softer spring, but I don't have one on hand at the moment.... It sure shows the benefit to an SSG over a conventional setup, though.... With the ability of this gun to be filled safely to 3500 psi, I should now be able to get two 10-shot mags on a single fill, which at 56 FPE is pretty impressive....

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 Apr 22, 2017 12:09 am 
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Location: Caronport, Saskatchewan
A real pleasure to read each stage of your projects Bob, you lay everything out so well! It's a real contribution to the sport of modding airguns that many will get inspiration from for many years. When everything is explained so well it almost makes a person feel like they are there with you enjoying the adventure and recording your findings. Thanks again, for myself and so many others who read your posts on this forum and the other forums you share your projects on. Sure makes a guy want to get in the shop and start tinkering, that's for sure!

Sent from my LG-H812 using Tapatalk

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