BPCR Exterior Ballistics
Posted: Wed Apr 08, 2015 1:16 am
BPCR Exterior Ballistics
Gents,
As some of you know, BPCR exterior ballistics has been a fascination of mine for the past 17 years. Pre-BPCR, HP, SB and air rifle exterior ballistics were a serious focus and fascination. Today I exchanged emails with a friend about the subject and thought I'd share some of what I sent to my buddy as well as a bit more.
-----------------------------------------------
After many rounds down range from 10 to 1,000 yards during testing for bullet stability and BC, I can say a few things that I'm confident are true.
1. Typical GG's (Jones, Brooks, etc.) will cause enough drag so as to require about 12 more MOA from the 1,000-yd line than a similarly shaped bullet with no GG's. MiniGG's only require about 4 more MOA than a GG'less bullet. MicroMiniGG's act like they are not there. They shoot the same trajectory as a bullet with no GG's. Extensive, live-fire testing from the 1,000-yd line was undertaken to draw the above conclusions. Numerous moulds were altered to support my assertions. Here's a picture of the two bullets used to test one of my hypotheses: MicroMini GG's act like they are not there, as the bullets fly downrange. Both moulds by Paul Jones using the same nose cutter.
2. Nose shape matters quite a bit when launching BPCR bullets fast, not so much when launching them slowly. Launching an optimally-designed bullet for and at high MV will substantially reduce the effects of head and tail winds. Recoil is the main limiter, IMHO, with regards to how fast one launches a bullet. The Money Bullet design was optimized to launch at 1,350 fps or slower. If a Creedmoor or Postell bullet is launched that fast, the reduction in the effects of head/tail winds is not much, but one will collect quite a bit of recoil for launching them that fast. Even the ODG's admonished long-range shooters to launch their bullets as fast as they could tolerate the recoil. The difference between a PJ Creedmoor and PJ Money Bullet, from the 1,000-yd line is about 9 MOA in favor of the Money Bullet, for just the nose effect, GG's not included in the estimate.
3. At 500 meters, a PP elliptical bullet will shoot about 1-to-1.5 MOA flatter than a PP Money Bullet when both weigh the same, have the same MV and are shot from the same rifle. Here's a picture of both bullets used in the testing.
4. The exterior ballistics of the PJ Creedmoor vs a PJ Money Bullet, both 45-cal, weighing 540 grains, showed some startling results. The Creedmoor bullet requires about 25% more wind correction in long-range matches. That assertion comes from years of coaching top shooters using those bullets. Testing from the 1,000-yd line by a friend and I, independently, showed that the Creedmoor required about 20 MOA more elevation than the Money Bullet. Both of us used 45-70 Brownings that launched both bullets with 75.0 grains of Swiss 1.5.
5. Bullet stability is key. An under-stabilized bullet will be deflected by the wind much more that a similar, slightly shorter/lighter bullet that is optimally stabilized. And, if the bullet is too under-stabilized, wild flyers will abound. I shortened a number of moulds by 0.025" at a time for this type of testing. A little shorter than optimum is better than a little longer than optimum.
6. My buddy and I have actually done dual-chronograph, BC testing. I did quite a bit more after we first did testing before the 2004 World Championships at Raton. There is a system I developed about 10 years ago that can measure average BC out to 1,000-yds. Preliminary testing was done at 500 meters with good results. One of these days I just might go there again. Here are the results from the 196 yard, dual-chronograph testing we did at Raton.
45-cal, 517-gr, Brooks Government Bullet = 0.396 BC
45-cal, 550-gr Brooks Creedmoor = 0.420 BC
45-cal, 580-gr Hoke LR = 0.450 BC
38-cal, 404-gr Brooks GG'less = 0.580
35-cal, 360-gr Brooks GG'less = 0.610
Gents,
As some of you know, BPCR exterior ballistics has been a fascination of mine for the past 17 years. Pre-BPCR, HP, SB and air rifle exterior ballistics were a serious focus and fascination. Today I exchanged emails with a friend about the subject and thought I'd share some of what I sent to my buddy as well as a bit more.
-----------------------------------------------
After many rounds down range from 10 to 1,000 yards during testing for bullet stability and BC, I can say a few things that I'm confident are true.
1. Typical GG's (Jones, Brooks, etc.) will cause enough drag so as to require about 12 more MOA from the 1,000-yd line than a similarly shaped bullet with no GG's. MiniGG's only require about 4 more MOA than a GG'less bullet. MicroMiniGG's act like they are not there. They shoot the same trajectory as a bullet with no GG's. Extensive, live-fire testing from the 1,000-yd line was undertaken to draw the above conclusions. Numerous moulds were altered to support my assertions. Here's a picture of the two bullets used to test one of my hypotheses: MicroMini GG's act like they are not there, as the bullets fly downrange. Both moulds by Paul Jones using the same nose cutter.
2. Nose shape matters quite a bit when launching BPCR bullets fast, not so much when launching them slowly. Launching an optimally-designed bullet for and at high MV will substantially reduce the effects of head and tail winds. Recoil is the main limiter, IMHO, with regards to how fast one launches a bullet. The Money Bullet design was optimized to launch at 1,350 fps or slower. If a Creedmoor or Postell bullet is launched that fast, the reduction in the effects of head/tail winds is not much, but one will collect quite a bit of recoil for launching them that fast. Even the ODG's admonished long-range shooters to launch their bullets as fast as they could tolerate the recoil. The difference between a PJ Creedmoor and PJ Money Bullet, from the 1,000-yd line is about 9 MOA in favor of the Money Bullet, for just the nose effect, GG's not included in the estimate.
3. At 500 meters, a PP elliptical bullet will shoot about 1-to-1.5 MOA flatter than a PP Money Bullet when both weigh the same, have the same MV and are shot from the same rifle. Here's a picture of both bullets used in the testing.
4. The exterior ballistics of the PJ Creedmoor vs a PJ Money Bullet, both 45-cal, weighing 540 grains, showed some startling results. The Creedmoor bullet requires about 25% more wind correction in long-range matches. That assertion comes from years of coaching top shooters using those bullets. Testing from the 1,000-yd line by a friend and I, independently, showed that the Creedmoor required about 20 MOA more elevation than the Money Bullet. Both of us used 45-70 Brownings that launched both bullets with 75.0 grains of Swiss 1.5.
5. Bullet stability is key. An under-stabilized bullet will be deflected by the wind much more that a similar, slightly shorter/lighter bullet that is optimally stabilized. And, if the bullet is too under-stabilized, wild flyers will abound. I shortened a number of moulds by 0.025" at a time for this type of testing. A little shorter than optimum is better than a little longer than optimum.
6. My buddy and I have actually done dual-chronograph, BC testing. I did quite a bit more after we first did testing before the 2004 World Championships at Raton. There is a system I developed about 10 years ago that can measure average BC out to 1,000-yds. Preliminary testing was done at 500 meters with good results. One of these days I just might go there again. Here are the results from the 196 yard, dual-chronograph testing we did at Raton.
45-cal, 517-gr, Brooks Government Bullet = 0.396 BC
45-cal, 550-gr Brooks Creedmoor = 0.420 BC
45-cal, 580-gr Hoke LR = 0.450 BC
38-cal, 404-gr Brooks GG'less = 0.580
35-cal, 360-gr Brooks GG'less = 0.610