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All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: mackeral5 on March 13, 2021, 01:39:31 PM
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I am mulling over the idea of building a 35" .357 barrel for my multi-caliber Bulldog. Primary bullet this barrel would shoot is the one cast from NOE's 359-174-FN-CE2 BT mold.
Planning (hoping!) to push the 174gr in the 1050fps MV range... pretty sure 950fps will be easily attainable, but hoping for 1050fps without having to run the pressure too high.
Normally when seeking a .357 barrel I go to the TJ's 1:26, but I believe this application may call for a slightly faster rate of twist.
I prefer TJ's .500 OD liners as I have a set of operations that make for easy DIY install into the Bulldog platform.
TJ's offers 1:26 and a 1:16. I am thinking the 1:26 may be a little slow and the 1:16 a little too fast.
Please share your experience and thoughts.
Thank you!
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When I designed that bullet, the Kolbe calculator said the optimum twist rate was 20-22".... However, a flat base bullet of the same design (without the boattail) would use a 26-28" twist as optimum.... The Kolbe calculator usually overestimates the loss of stability of my Bob's Boattails, they are almost always stable in a bit slower twist than predicted, and quite often stable in a twist rate that Kolbe recommends for a flat-based version, particularly if the boattail is not too extreme, which is the case for that design (the boattail was shortened from an earlier drawing to lighten the bullet).... Bottom line is, if you have a 26" twist TJ's barrel, I would try it, I think it may be fine....
Bob
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When I designed that bullet, the Kolbe calculator said the optimum twist rate was 20-22".... However, a flat base bullet of the same design (without the boattail) would use a 26-28" twist as optimum.... The Kolbe calculator usually overestimates the loss of stability of my Bob's Boattails, they are almost always stable in a bit slower twist than predicted, and quite often stable in a twist rate that Kolbe recommends for a flat-based version, particularly if the boattail is not too extreme, which is the case for that design (the boattail was shortened from an earlier drawing to lighten the bullet).... Bottom line is, if you have a 26" twist TJ's barrel, I would try it, I think it may be fine....
Bob
Bob, thank you for the quick response. I do not currently have the barrel, it will be a new purchase/build. If I am interpreting you correctly, a flat based bullet of similar length/design would be fine in the 1:26? I could always have the mold decked a little bit or run a different flat-based bullet of similar length.
Do you have an opinion of what is the lightest bullet you think would do well with TJ's 1:16 liner?
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I have an LW barrel in .357, which is a 16" twist.... It seems to shoot 125-154 gr. bullets OK.... but to be truthful I have never really pushed the range.... It's going to depend more on the exact bullet, rather than the weight/length, I think....
Bob
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You know after sending this I realized I could just test in my 29" 1:26 barrel and push it as hard as I can to try and get the velocity up. Just enough shots to see if it wants to group or patterns like a shotgun.
If my local compressed gas company gets restocked on nitrogen this week I'll do some testing.
The 1:16 twist is scary fast to me in .357, I don't think I will take that leap of faith without anyone sharing first hand experience pushing 1000fps MV out to 100 yards....
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You know after sending this I realized I could just test in my 29" 1:26 barrel and push it as hard as I can to try and get the velocity up. Just enough shots to see if it wants to group or patterns like a shotgun.
If my local compressed gas company gets restocked on nitrogen this week I'll do some testing.
The 1:16 twist is scary fast to me in .357, I don't think I will take that leap of faith without anyone sharing first hand experience pushing 1000fps MV out to 100 yards....
I was just researching this 'faster twist rate in a .357' because of those new Russian barrels being offered in a 390 twist rate by alfa-precision.net. They are just over 15.3" twist rate, and I am using the 1:26" twist with decent results at over 200 yards. I use the NSA 142 grain HP-BT currently, and exclusively, because cast bullets were not MOA accurate out at long range.
With the 390 twist barrel would you think by getting the FPS up to 960 or more that it would stabilize better? What about if only pushed in the lower 900fps range? And, does a faster twist barrel require a longer bullet?
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You know after sending this I realized I could just test in my 29" 1:26 barrel and push it as hard as I can to try and get the velocity up. Just enough shots to see if it wants to group or patterns like a shotgun.
If my local compressed gas company gets restocked on nitrogen this week I'll do some testing.
The 1:16 twist is scary fast to me in .357, I don't think I will take that leap of faith without anyone sharing first hand experience pushing 1000fps MV out to 100 yards....
I was just researching this 'faster twist rate in a .357' because of those new Russian barrels being offered in a 390 twist rate by alfa-precision.net. They are just over 15.3" twist rate, and I am using the 1:26" twist with decent results at over 200 yards. I use the NSA 142 grain HP-BT currently, and exclusively, because cast bullets were not MOA accurate out at long range.
With the 390 twist barrel would you think by getting the FPS up to 960 or more that it would stabilize better? What about if only pushed in the lower 900fps range? And, does a faster twist barrel require a longer bullet?
I am by no means very informed in this area. However, I have personally seen that too much velocity and too fast of a twist with too short of a projectile will make a gun go from grouping to patterning like a shotgun.
My guess is to take advantage of that 15.3" twist would require very heavy, very long bullets. Or velocities that aren't a good match for long range shooting.
That NSA 142gr and TJ's 1:26 are close to a perfect match....
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Somewhat of an update. I converted back from .257 to .357, which is a matter of changing barrels and probes. The only issue is my .257 barrel is 35" long and setup to run a 500cc high pressure tube. My current .357 1:26 barrel is only 29". This means I cannot run a suppressor due to the tube being longer than the barrel....and without a suppressor I can't do any real target shooting while at the same time being respectful of my neighbors. I have another OEM length high pressure tube in route, so hopefully later in the week I can see how the 174gr will group.
But, indoors with hearing protection I have been able to do some chronograph testing... When the gun was in .257 format I identified 2 issues that were limiting power a bit---hammer weight and too short of poppet stem protrusion. The stem protrusion was resolved by making up another poppet and I made a 17gram brass spring guide/hammer weight. total hammer weight is right at 120grams now.
After converting to .357 these changes moved the chains out a bit on max power. Previously the most I had ever seen was somewhere around 979fps with 162gr. Today at 3600psi it maxes out with 174gr consistently in the 998-1003fps range. I should be able to get a 3-5 shot tune in the 950fps range, that will be good enough to do some accuracy testing.
Based on what I am seeing so far, I am fairly certain that a 35" 1:26 barrel will soon be on order. Even if the 174gr isn't a good combination with the 1:26 barrel, I can always dial it down for a mild yet powerful tune with something like the NSA 142gr.
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The smaller tube makes a big difference in energy potential. I previously saw that at lower pressures and power levels. There is simply no substitute for minimizing pressure drop during the shot With 340cc vs 500cc and not investing too much effort all I was able to find was a 3 shot tune averaging 935fps. Current barrel length is 29.5" from port to muzzle.
Here is a target of 3 shot groups using 174gr cast and sized to .357. I did not weigh nor sort, this was just intended to somewhat coarse of testing to see if the twist and bullet at least worked ok with each other. Based on previous experience there is around 1-1.5gr spread in weight amongst this batch of bullets.
Distance is 75 yards, the farthest I can safely shoot at these energy levels.
(https://i.imgur.com/rsbBzKo.jpg)
Based on this relatively small data set, I would not hesitate to combine the 174gr BBT with a 1:26 TJ's barrel. Next week I will be ordering 36" of 1/2 OD 1:26.
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I see NO sign of tumbling.... I would definitely go with the 26" twist barrel....
Bob
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I see NO sign of tumbling.... I would definitely go with the 26" twist barrel....
Bob
Yes, very encouraging results.
As a sidenote... This is my .257/.357 Bulldog. For the caliber conversion, all I did was replace the .257 barrel/probe with the .357 barrel/probe and make an HST adjustment. Would you believe the same scope zero for the .257 at 102 yards was basically dead on for the .357 at 75? I fully expected to have to dial it in, but no scope adjustments were required.