Canadian Airgun Forum https://www.airgunforum.ca/forums/ |
|
Small Caliber PCP Varmint Rifles https://www.airgunforum.ca/forums/topic81955.html |
Page 1 of 2 |
Author: | rsterne [ Sun Feb 03, 2019 8:44 pm ] |
Post subject: | Small Caliber PCP Varmint Rifles |
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.... 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.... 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.... 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.... 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 |
Author: | Daryl [ Tue Feb 05, 2019 2:51 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
My hat's off to you, Bob - those rifles are phenomenal. |
Author: | rsterne [ Tue Feb 05, 2019 4:03 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
Well I figure for ground squirrels, .17 or .22 cal should be enough.... bob |
Author: | Daryl [ Tue Feb 05, 2019 4:22 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
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. |
Author: | FRANK [ Tue Feb 05, 2019 5:46 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
I was thinking of a 950fps 16 grains in .177 for Varmint or even the 21 grains piledriver |
Author: | rsterne [ Tue Feb 05, 2019 7:18 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
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 |
Author: | Daryl [ Wed Feb 06, 2019 3:16 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
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. |
Author: | rsterne [ Wed Feb 06, 2019 4:35 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
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 |
Author: | Daryl [ Fri Feb 08, 2019 4:13 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
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. |
Author: | rsterne [ Fri Feb 08, 2019 7:51 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
CrMoly, don't know if 4130 or 4140.... Bob |
Author: | Daryl [ Fri Feb 08, 2019 11:19 pm ] |
Post subject: | Re: Small Caliber PCP Varmint Rifles |
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. |
Page 1 of 2 | All times are UTC - 5 hours |
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group http://www.phpbb.com/ |