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PostPosted: Sun Feb 03, 2019 8:44 pm 
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Location: Coalmont BC
Last year I built two PCPs, a 6mm regulated and a .257 cal unregulated.... This year I have a .172 cal barrel for the 6mm and a .224 cal barrel for the .257.... They are both TJ's with a 14mm OD and a 9" twist, and I have the same 14mm ID x 20m OD Carbon Fibre Sleeves for them as I used on last years builds.... Here are the two rifles I am starting with.... The 6 mm is regulated at 2800 psi, with the 165 cc plenum made from 2024-T3 with a 0.095" wall, fed from a 500 cc 4500 psi Carbon Fibre bottle.... It is tuned for 125 FPE with bullets from 61-73 gr.... with a maximum of 136 FPE....

Image

The .257 is unregulated with a MSWP of 4300 psi, but I plan to run it at 3800 psi, the same as I am currently in .257.... It has a 300 cc 2024-T3 reservoir with a 0.120" wall.... It is tuned for 165 FPE with 80-92 gr. bullets, and peaks at 201 FPE....

Image

Both guns have my own version of the SS Valve, and MDS hammers with an 11 lb/in. spring and are very easy to cock.... They are both fitted with harmonic tuning weights on the muzzle, which I plan to fit to the new barrels as well.... The receivers are interchangeable on the lower assemblies.... If you want to read about the original builds, you can do so here.... Before you ask, I have not yet done any accuracy testing of either gun, the Motel prevents me from doing any shooting in the summer, so serious testing will have to wait until 2021, after we retire.... ::)

topic76526.html

When the new barrels are fitted I will have four calibers, and all can be shot regulated at 2800 psi or unregulated at 3800.... although I plan mostly to use the .172 regulated and the .224 unregulated.... I currently only have one bullet for each caliber, I have a HP version of the 27 gr. NOE 172-26 which weighs 24.7 gr.... and the FN version of the NOE 225-61 which weighs 61 gr.... I have already made chamber reamers and cut the chambers in the TJs barrels, you can see what that process was like in this thread....

topic81940.html

Today I got a good start on fitting the new barrels.... I made two new bolts and loading trays, one in each caliber.... Here they are, along with the bullets....

Image

I made the receivers with a 1/2" bore for the bolt and barrel, so it is pretty easy to change calibers by making the above parts.... The loading tray is fastened into the receiver with a single flat-head 4-40 screw.... The receiver is shown below, you can see the threaded hole for that 4-40 screw in the loading bay in the upper receiver....

Image

The receiver is only notched out for loading on the right.... leaving the left side full height for increased rigidity.... They are both equipped with a velocity adjusting screw on the back which pushes a steel pin forward to prevent the bolt from being fully retracted in the J-slot.... This allows easy adjustment of the velocity without changing the hammer strike or pressure.... Since that capability is built into the receivers, it will also be available in the two new calibers.... This means I can leave the guns tuned for the larger calibers, and just choke up the porting if I have too much power.... The next step will be to machine the barrels to fit the receivers, and machine the barrel ports, transfer port recesses, and grooves for the O-rings to seal the breech....

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 Feb 04, 2019 6:32 pm 
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Today I worked on the breech end of the barrels.... First I machined the O-ring grooves, checking as I went to make sure I got the groove the proper depth to get a nice sliding fit on the bolt.... I used a #009 O-ring on the .224 cal and a 4 mm ID x 6.4 mm OD x 1.2 mm CS O-ring on the .172 cal.... I had to grind down the internal grooving tool I had made previously for that CS Metric O-ring as it was too large in diameter to fit inside the tiny bore.... These were time-consuming to make, but went well and I am pleased with the results....

Image

I also laid out and machined the barrel ports and the 3/8" flats for the transfer ports to seal against.... Both barrel ports are oblong to get full bore area without exceeding 80% of the caliber for the width of the port.... The .224 cal port is 0.176" wide and 0.27" long, and the .172 cal port is 0.136" wide and 0.26" long at the boreline…. Both start at 0.257" at the transfer port face, to match up to the transfer port ID, and are blended from round to oblong within the thickness of the barrel wall....

This was a long day requiring a lot of concentration, so I am putting off threading the muzzle end for the harmonic tuners for another day.... Once that is done I will be able to cut the carbon fibre sleeves to length and glue them onto the barrels.... This project is moving along quite nicely.... 8)

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 Feb 05, 2019 2:51 pm 
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Location: P.G. B.C.
My hat's off to you, Bob - those rifles are phenomenal.

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Daryl


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PostPosted: Tue Feb 05, 2019 4:03 pm 
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Well I figure for ground squirrels, .17 or .22 cal should be enough.... :lol:

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 Feb 05, 2019 4:22 pm 
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I hope to test out the Condor on gophers this coming spring. Should work to about 100yards. We usually restrict the .22LR's to that range,
then use the HMr's to 200 and the CF .17's after that.

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Daryl


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PostPosted: Tue Feb 05, 2019 5:46 pm 
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Location: 1/2 Way From Ottawa and Montreal,
I was thinking of a 950fps 16 grains in .177 for Varmint
or even the 21 grains piledriver

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PostPosted: Tue Feb 05, 2019 7:18 pm 
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Well Cedric (Tofazfou) has used this NOE 25 gr. HP at 960 fps on ground squirrels and prairie dogs, and says it's devastating....

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 Feb 05, 2019 9:12 pm 
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Location: Coalmont BC
Today I threaded the muzzles 1/2"-20 NF to accept my harmonic tuners.... I can also use a Hatsan Air Stripper, should they become available again.... I then cut the Carbon Fibre sleeves to length.... They are 14mm ID x 20mm OD, so once installed the barrel will be over 3/4" OD.... I sanded and cleaned the barrels and the inside of the sleeves, and installed them with Loctite 638.... Here is what the muzzle looks like, without the tuner in place....

Image

After an overnight cure at room temperature, I will give them a post cure in my wife's oven at 175*F for 3 hours.... Then I can finish fitting the OD of the sleeve to the receiver and drill the 6 holes through each sleeve for the setscrews so that they bite against the steel of the barrel when installed....

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 Feb 06, 2019 3:16 pm 
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Location: P.G. B.C.
Bob - I see the .172" is 9" twist. May I ask, what is the outside diameter of these as received?
How much? What is their rating for pressure? I am thinking of liners chambered for the .17HMR.
If .172" groove dia. they must be at least RF barrels or liners, ie: 24,000psi minimum.
tks.

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PostPosted: Wed Feb 06, 2019 4:35 pm 
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The liners/barrels I got from TJs are 14mm OD (0.550")…. He normally makes them in 1/2" (or can do 3/8" or 9/16" in .172 cal, and 7/16" or 9/16" in .224 cal), but I had him hammer the 9/16" OD down to 14mm to fit the CF tubing I could get.... Same thing with the 6mm and .257 cal barrels I got last year, they are normally 1/2" or 9/16", I had him hammer the larger size down to 14mm.... I turn the breech and muzzle ends down to 1/2"....

You could get the barrels in 1/2", and then get 1/2" ID x 3/4" OD CF tubing from the USA, but it's a lot more expensive than the (beautifully made) 14 x 20 mm Metric tubing from China.... plus this way the OD is a bit larger, so the barrel is stiffer.... The 0.550" OD CrMoly barrel in .172 cal would have a 3:1 safety margin at 27,000 psi.... the .224 cal would be 3:1 at 23,000 psi.... These do not allow for a larger chamber diameter, just based on the bore, 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!


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PostPosted: Thu Feb 07, 2019 7:02 pm 
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Location: Coalmont BC
Yesterday I did a post-cure on my barrel sleeves, crowned the muzzles, and lapped the bores with JB Bore Paste and then polished them with Bore Brite.... Today I turned down the breech end of the sleeves a few thou to fit into the receivers.... Once that was done, and the barrels could be slid into place, I marked and drilled the locations for the six setscrews in each barrel, fitting the .224 cal. barrel to the .257 receiver and the .172 cal. barrel to the 6mm receiver.... I use a SHCS drilled though with a 1/8" hole for a drill guide, which I install in each hole and then run the drill down to drill through the sleeve to the barrel....

Image

After marking all six holes, I then enlarge the holes with a 3/16" drill, removing all the CF to that diameter and leaving a shallow pocket in the steel of the barrel for the setscrew to bite into.... Here is what the finished barrels look like....

Image

You will notice that the O-rings are in place in the groove in the breech end of each barrel.... I checked the length of each bolt nose when retracted into the J-slot, and shortened them flush with the back of the barrel port.... They load the base of the bullet just past the front of the barrel port, then you pull it back into the lower slot to remove all obstruction to flow.... That retraction distance can be decreased with the velocity adjusting screw on the back to force the bolt nose to partially obstruct the barrel port....

After lunch, I checked everything over and fitted the .172 cal upper to the regulated lower.... The transfer port was the proper length, so I was able to take a few shots.... I didn't change the SSG adjustment from the last time I shot the 6mm, and by measurement it was set at 8 turns of gap.... Even so, those tiny 24.7 gr. bullets screamed across the Chrony at 1060-1070 fps.... What really shocked me was how quiet the gun was.... Mind you, the last few times I tested in the shop I was shooting a .357, but even so, the report was very low.... Not what you would get with some assistance from a can or shroud.... but they are illegal in Canada anyways....

I then removed the .172 cal upper and fitted the .224 cal one.... Once again, the existing transfer port length was fine, so a took a few shots.... With the 61 gr. bullets I intend to shoot in the unregulated version the velocity was only 775 fps.... so I tried some of the 47.6 gr. Bowmans and they shot a very respectable 930 fps at the 2800 psi regulator setting I am using on this lower assembly.... That's a bit less than I was getting in my .224 cal Hayabusa with the same bullets, but that was shooting at 3000 psi.... and as I said, I never even touched the SSG gap, it was still set for whatever tune I last had for the 6mm.... The .224 was noticeably louder than the .172.... so I guess it really was that quiet.... 8)

I have a leak to chase down in the unregulated lower assembly, it was empty when I pulled the .257 upper assembly off.... The bottle on the regulated lower assembly, on the other hand, was still sitting at 3600 psi, which is about where it would have been when I put it away months ago.... In fact, I never added any air to it for todays initial testing.... I am delighted with todays results, and over the next few days I will do some proper testing to explore both the upper power limits and the efficiency of both the .172 cal. and .224 cal. uppers on the 2800 psi regulated lower assembly.... Testing the .224 (and probably the .172 as well) at 3800 psi unregulated will have to wait until I find and fix that leak.... :roll:

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: Fri Feb 08, 2019 4:13 pm 
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Location: P.G. B.C.
TKs for the answers, Bob. Good work on those. Forgot to ask, do you know the steel he uses?

Normal Chromoly bl. steel at 4140 or 4150 would have considerably higher PSI rating, seems to me.

Too- it is much harder machining than stainless or 1130 RF & BP rifle CTG. barrel steel as sold by Green Mountain.

If they are 1130 - they would do for a .17HMR for sure.

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Daryl


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PostPosted: Fri Feb 08, 2019 7:51 pm 
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CrMoly, don't know if 4130 or 4140....

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 Feb 08, 2019 11:19 pm 
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Location: P.G. B.C.
Thanks, either would be OK for a HMR in 1/2" or .550" I am sure.
I'm thinking of re-barreling a Savage .17HMR that did not shoot as well as I thought it should.
Now have to find some contact information.
The GTA site wasn't much help- so far.

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Daryl


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PostPosted: Sat Feb 09, 2019 7:25 pm 
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I tested both barrels today, first on the regulated lower at 2800 psi, and then on the unregulated lower, tethered at 3800 psi.... First, are the results regulated....

Image

The .172 cal HP maxed out at 1060 fps (61.6 FPE), and at this pressure I was not really able to dial the velocity down much.... With 8 turns of SSG gap it was still shooting 1050 fps, but it only used 300 psi from the 500 cc (30.5 CI) bottle for 10 shots, ie just 30 psi per shot.... That should mean between 50-60 shots per fill.... I can dial the velocity down by using the velocity screw on the back of the receiver.... Screwing that in 6 turns drops the velocity to 980 fps....

I used a 45.0 gr. bullet when testing the .224 cal at this pressure.... It maxed out at 1010 fps (102 FPE)…. This was more out of curiousity, because the intended use of that barrel is with a heavier bullet in the unregulated version at 3800 psi.... Here are the results at that pressure....

Image

As you can see, with the 61 gr. bullet the gun peaked at 997 fps (135 FPE), and had a normal tuning range of about 200 fps, as can be expected with an SS valve operating within its design range.... At 6 turns of gap, the velocity was 960 fps, and 5 shots averaging 125 FPE used 400 psi from the 300 cc (18.3 CI) reservoir, which works out to 1.24 FPE/CI.... This gave a short string starting from 3800 psi, with the first 4 shots within 11 fps, dropping another 11 fps on the 5th shot (less than a 3% ES)…. This means I can tether at 3800 psi and expect that kind of performance with the tether removed, which is just about perfect for my use....

I tested the .172 cal upper, just out of curiousity, at 3800 psi, and it was just shy of 1200 fps.... peaking at 1184 fps (77 FPE)…. Dialed back to the minimum practical with this valve, it was barely subsonic, at 1120 fps.... :o

So, this project ended up right where I wanted it for the .224 cal version.... The .172 cal is maybe a bit hot, I'll have to see how it shoots at 1050 fps, compared with dialed down a bit with the velocity adjuster.... If it ends up shooting better in the mid 900s, then it would be best to reduce the setpoint pressure, but since the regulated lower is shared with the 6mm barrel, and that shoots right where I want it at 2800 psi, I will just dial the velocity down by restricting the barrel port with the velocity adjuster if necessary....

I am delighted with the way this project turned out.... I now have 4 calibers interchangeable between the 2800 psi regulated lower and the 3800 psi unregulated lower.... I hope they end up as accurate as they are powerful....

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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