Who Makes Custom 20 Caliber bullets?
- Thread starter Terry
- Start date
Thank you Sherm - that's what I thought - I'd have expected to pressure out before attaining that velocity via RL-15.
What follows is an attempt to help people decide on barrel twist rate for the longer/heavier bullets.
Here are pics of some 40 & 53 Gr. BT, .20 Cal. bullets. Note that the length of the 53 Gr. version is 0.837”, or, 4.103 calibers long. The me’plat diameter is 0.045”. As calculated on the Tioga Engineering Bullet Design program, this bullet, at 3500 FPS, for a gyroscopic stability factor (Sg) of 1.5,@sea-level, Std. conditions, requires a twist rate of 1:8.4”. A 1:9” twist barrel will result in Sg1.3 - weak, but not quite, “a wreck”. A longer & lighter bullet will need a somewhat faster twist. Sg of less than 1.4 will not get all of the potential BC the bullet has to offer. Tioga predicts a BC (G1) of .39 - in my experience, calculated BC seldom holds up - in the real-world: subtracting 0.010 - 0.015 is a realistic expectation; .375 - .38 will probably prove close.
For those who use the readily available, and accurate, JBM drag/twist calculator (not the Miller formula, which the last time I compared it, still had some bugs to work out) here are the vital inputs, in calibers: length = 4.103; nose length = 2.863; BT length = .417; BT end diameter = .823; specific gravity = 10.4; me’plat diameter = .220. Compare at a close velocity, and you’ll be within 0.10” of twist rate requirement.
You can input somewhat varying lengths, leaving specific gravity, BT length and angle (or, end diameter), and me-plat diameter and get a reasonably close idea of what you need. The Tioga Bullet Design (the late, William C. Davis Jr.) & the McCoy based Drag/Twist calculator invariably produce twist rate within 0.1". When they do not correlate, something is, "out of whack".
RG
Ooops - It's important to determine, and enter the correct, or close to it, specific gravity,
as this accommodates the program in calculating the balance & the overturning moment - what I found lacking in the Miller program - but that could have been corrected by now.
What follows is an attempt to help people decide on barrel twist rate for the longer/heavier bullets.
Here are pics of some 40 & 53 Gr. BT, .20 Cal. bullets. Note that the length of the 53 Gr. version is 0.837”, or, 4.103 calibers long. The me’plat diameter is 0.045”. As calculated on the Tioga Engineering Bullet Design program, this bullet, at 3500 FPS, for a gyroscopic stability factor (Sg) of 1.5,@sea-level, Std. conditions, requires a twist rate of 1:8.4”. A 1:9” twist barrel will result in Sg1.3 - weak, but not quite, “a wreck”. A longer & lighter bullet will need a somewhat faster twist. Sg of less than 1.4 will not get all of the potential BC the bullet has to offer. Tioga predicts a BC (G1) of .39 - in my experience, calculated BC seldom holds up - in the real-world: subtracting 0.010 - 0.015 is a realistic expectation; .375 - .38 will probably prove close.
For those who use the readily available, and accurate, JBM drag/twist calculator (not the Miller formula, which the last time I compared it, still had some bugs to work out) here are the vital inputs, in calibers: length = 4.103; nose length = 2.863; BT length = .417; BT end diameter = .823; specific gravity = 10.4; me’plat diameter = .220. Compare at a close velocity, and you’ll be within 0.10” of twist rate requirement.
You can input somewhat varying lengths, leaving specific gravity, BT length and angle (or, end diameter), and me-plat diameter and get a reasonably close idea of what you need. The Tioga Bullet Design (the late, William C. Davis Jr.) & the McCoy based Drag/Twist calculator invariably produce twist rate within 0.1". When they do not correlate, something is, "out of whack".
RGOoops - It's important to determine, and enter the correct, or close to it, specific gravity,
as this accommodates the program in calculating the balance & the overturning moment - what I found lacking in the Miller program - but that could have been corrected by now.
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Not trying to imply that a 1:9" will not work - simply, that, according the the GURUS calculators, and parameters, a 9" twist rate will not fully stabilize bullets ("put them to sleep") of that length - not at any velocity. I am neither mathematician, nor ballistic guru - I have used the Tioga program without failure since I first acquired a computer: I have come to trust it.
Even for - make that, especially for - competition bench-rest rifles/cartridges, once I accepted the 1.5 Sg concept, I have been successful. The goal is to help people from spending their $$ on marginal stuff - especially important when opting for button-rifled barrels. The only time I get concerned with too fast a twist rate, is when the potential for molten cores and jacket failure is likely . . . sadly, that is most often discovered empirically.
RGNot trying to imply that a 1:9" will not work - simply, that, according the the GURUS calculators, and parameters, a 9" twist rate will not fully stabilize bullets ("put them to sleep") of that length - not at any velocity. I am neither mathematician, nor ballistic guru - I have used the Tioga program without failure since I first acquired a computer: I have come to trust it.
Even for - make that, especially for - competition bench-rest rifles/cartridges, once I accepted the 1.5 Sg concept, I have been successful. The goal is to help people from spending their $$ on marginal stuff - especially important when opting for button-rifled barrels. The only time I get concerned with too fast a twist rate, is when the potential for molten cores and jacket failure is likely . . . sadly, that is most often discovered empirically.
Really?? Well it is only a computer and guess what.... it is wrong. Here ya go... 9 twists will stabilize 55 grain pills in a 20 cal just fine out past 1000
http://www.accurateshooter.com/guns-of-week/gunweek0103/
does your observed drop for the 55s match with a ballistic calculators estimates for drop with the 55s and your velocity?
L.Sherm
Silver $$ Contributor
I can't confirm that, the scope I had on it was a older bushnell elite with only 1/8 m.o.a. elevation adjustment and I didn't have a rail on it so I ran out of elevation to dial it to center bull. I just held for center bull to see how it shot. I have a 36x power scope with a 20 m.o.a rail now but have not made it out with it again. I built this gun for 2 reasons one to see how the 9tw. Stabilized and just how fast I could push the 55's and shoot accurate. I never did find the pressure wall per say it just shot so well in mine at 3750 I left it there. I still have some seating depth testing to do at that 500yds range. I know it could be even better. Is it a BR caliber well I don't kow about that but it is one fine longer range caliber for a 20 cal.
Yes, really!
Note that I did not suggest unstable, but rather marginally stable, which means that you are giving up BC, which, I believe is the primaryreason for using/wanting the heavier 20 Cal. bullets.
RGI have yet to do actual drop testing for the 53 Gr. BT - waiting on a 1:8" twist PacNor SSSM. Once I get that, and can compare to the 1:9" that I already have, I'll be able to provide a, "real-world", comparison.
The info above, was "computed" using a Tioga Bullet Design program, I just chose to compare at 3500 FPS.
My experience has been, that even with a twist rate which produces a Std conditions Sg 1.5, the real-world BC is usually 0.010 - 0.015 lower than the "ideal" (calculated) BC, and when twist rate produces below 1.4 Sg, BC begins to measurably diminish. RG
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I agree with Sherm and my experience with 9 twist 20 caliber barrels matches his exactly. Those ballistic calculators from berger and others are only a small piece of the puzzle in my opinion, they offer you a direction but should not be used to make the entire decision on barrel twist rate. In the real world a 9 twist will stablize heavy 20 caliber bullets such as the Berger 55 just fine, I have tested it in multiple Temps and elevations as well. One could make the argument that the bc is not 100 optimized with the 9 twist and 55 berger combo, however I don't belive you will loose enough to be noticeable or measureable. That being said we all know that 20 calibers are not the best option for shooting out to a 1,000 yards anyways.
Since I have not been able to find a supply of jackets to make the 48gr bullets there is no point in getting to excited about them. I have though been able to get jackets to make a 46.5gr .204 bullet, I have been testing it in both 8 and 10 ogive and out of a couple of 11 twist 20 caliber rifles I have. In one rifle, a 20 Tac they shoot very well, out of my 9 twist 5/35 they shoot extremely well. I don't have a good idea what the BC is on this bullet, I do know that at 500yds there is no difference at all between a 8 or 10 ogive. They both drop the same and they both drift about 21 inches in a 15-20 mph right angle wind.
17VLD
Gold $$ Contributor
Nice looking bullets Randy.I look forward to when you have completed your testing with the 53.I have shot a lot of the 50 grain and 55 grain Bergers in my 20Dasher and always felt the 9 twist was on the edge for the 55.
Velocity wise I always wished for something closer to the 50 Berger,I proofed my 50 grain loads up to 4200fps then settled on a load that was right at 4100 for accuracy.The 50 Berger was very accurate with N-550,alas it is gone and it's b.c. was not as apealing as the 55s.I will rebarrel with an 8 twist once the 9 gives up. I live at 6202 feet elevation perhaps if things work out I can try some of your 53s.Say hi to Al Nyhus if you see him
Matt
Velocity wise I always wished for something closer to the 50 Berger,I proofed my 50 grain loads up to 4200fps then settled on a load that was right at 4100 for accuracy.The 50 Berger was very accurate with N-550,alas it is gone and it's b.c. was not as apealing as the 55s.I will rebarrel with an 8 twist once the 9 gives up. I live at 6202 feet elevation perhaps if things work out I can try some of your 53s.Say hi to Al Nyhus if you see him
Matt
Nice looking bullets Randy.I look forward to when you have completed your testing with the 53.I have shot a lot of the 50 grain and 55 grain Bergers in my 20Dasher and always felt the 9 twist was on the edge for the 55.
Velocity wise I always wished for something closer to the 50 Berger,I proofed my 50 grain loads up to 4200fps then settled on a load that was right at 4100 for accuracy.The 50 Berger was very accurate with N-550,alas it is gone and it's b.c. was not as apealing as the 55s.I will rebarrel with an 8 twist once the 9 gives up. I live at 6202 feet elevation perhaps if things work out I can try some of your 53s.Say hi to Al Nyhus if you see him
Matt
Will do, Matt - Al is doing well, but, at least for, "one more year", still racing!
Being way up there certainly doesn't hurt! I expect them, "to work" via as slow as 1:9". However, having acquired the draw/trim dies, and having made some bullets, thus, obtaining actual dimensions, I would not deliberately order a 9" twist for bullets this long. There is no down-side to calculating for Std. sea-level: that works everywhere! RG
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