BPCR Exterior Ballistics

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DanTDesigns
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BPCR Exterior Ballistics

Post by DanTDesigns »

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.
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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.

Image

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.

Image

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
All the best...DanT..."The nation which indulges towards another a habitual hatred or a habitual fondness is in some degree a slave.” - George Washington’s 1796 Farewell Address
mdeland
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Re: BPCR Exterior Ballistics

Post by mdeland »

Dan, I forget just now what the dimensions (width and depth) are on the micro-min groove as opposed to the mini-groove. Could you give them?
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Re: BPCR Exterior Ballistics

Post by DanTDesigns »

mdeland wrote:Dan, I forget just now what the dimensions (width and depth) are on the micro-min groove as opposed to the mini-groove. Could you give them?
Mike,

MiniGrooves are 0.050" wide and 0.020" deep

MicroMiniGrooves are 0.025" wide and 0.015" deep

One thing I found is that chromo barrels need more lube than stainless steel barrels to facilitate fouling control when using a blow tube. That might also be true if wiping, but I've not done any testing in that direction; so, it's just a hypothesis. Some shooters have had fouling control difficulties with these GG designs due to using rough, chromo barrels. The rougher the barrel, the more lube required for optimum fouling control. If wiping, guys using chromo barrels have found that using more of the NAPA oil in their wiping solution will help with leading. That was driven home in spades at the 2005 National Creedmoor trials at Raton when a friend was fouling out badly. Changing his wiping solution to 20% NAPA oil did the trick. Also, having MicroMini GG's in the boreriding section is a good idea if using chromo barrels. That will reduce the risks of leading on top of the lands. The research and testing to better understand how these things work has been an ongoing experiment in having fun:-))) Good shooting to all ya'll.
All the best...DanT..."The nation which indulges towards another a habitual hatred or a habitual fondness is in some degree a slave.” - George Washington’s 1796 Farewell Address
Jubilado
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Re: BPCR Exterior Ballistics

Post by Jubilado »

Very interesting. Thanks, Dan.

Sure addresses the question posed recently in another thread: "Why shoot a paper patched bullet?"

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SSShooter
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Re: BPCR Exterior Ballistics

Post by SSShooter »

Dan - is BACo's 40cal 400gr 409400M4 "Kidwell" bullet mold (your Money design) a mini-groove?
Glenn
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Re: BPCR Exterior Ballistics

Post by DanTDesigns »

SSShooter wrote:Dan - is BACo's 40cal 400gr 409400M4 "Kidwell" bullet mold (your Money design) a mini-groove?
Glenn,

I think it is. Kidwell would be the guy to ask because I've not measured any of the bullets from the mould.
All the best...DanT..."The nation which indulges towards another a habitual hatred or a habitual fondness is in some degree a slave.” - George Washington’s 1796 Farewell Address
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Re: BPCR Exterior Ballistics

Post by DanTDesigns »

SSShooter wrote:Dan - is BACo's 40cal 400gr 409400M4 "Kidwell" bullet mold (your Money design) a mini-groove?
Glenn,

Here's a diagram of a bullet I designed for Kidwell. This may be the 409400M4 "Kidwell" bullet. Kidwell should be able to confirm one way or the other.

Image
All the best...DanT..."The nation which indulges towards another a habitual hatred or a habitual fondness is in some degree a slave.” - George Washington’s 1796 Farewell Address
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deerhuntsheatmeup
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Re: BPCR Exterior Ballistics

Post by deerhuntsheatmeup »

Dan,

With all due respect to the other versions of the Money bullet, I sure do wish a mold maker would make a cutter with that 60% of caliber nose like Paul used to cut. Not that I need one yet, but someday I will.....

Also, as a side note, I now have the first .45 Money bullet from Paul, that came from you. AND the first .40 cal Money that Paul cut that I bought originally and sold, then bought back. FYI

Best, barvid
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Re: BPCR Exterior Ballistics

Post by Jim Kidwell »

Glenn,

That is the design of the BA 409400M4 bullet. I had Paul Jones make the same mould. His nose profile more closely follows Dan's nose diameter spec. The only thing I changed was the bottom driving bands to .409". I asked Dan to closely follow his original MicroMiniMoney (M³) bullet design, I had good success with. It held the 2@200 Pedersoli match record (best 1.141") four years in a row at Raton for the 40 Cal Scope. The M³ bullet launches at 1280 fps with 62 Gns. of Swiss 1 1/2. It shot 3-4 MOA less than the PJ Creedmoor (another great PJ design bullet) at 600 Yds. You do have to wipe with it due to the minimal lube capacity, especially at low humidity and high temps.........
Image
....................................Jim
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deerhuntsheatmeup
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Re: BPCR Exterior Ballistics

Post by deerhuntsheatmeup »

Jim, thanks for posting that dwg!

It is my opinion that the .400 bore riding section just ahead of the .402 band is what makes this bullet leave centered and fly so dang straight! But again, some rifles will digest well anything you feed it. Go figure!

Best, Barfield
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Re: BPCR Exterior Ballistics

Post by Jim Kidwell »

This is another Dan T. design elliptical bullet for a Ron Smith SS gain twist barrel (10-twist) for a 38-72................

Image
....................................Jim
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Don McDowell
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Re: BPCR Exterior Ballistics

Post by Don McDowell »

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
Boy Howdy, is that part ever true, and surprising overlooked by many...
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mdeland
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Re: BPCR Exterior Ballistics

Post by mdeland »

Dan, I wonder if the less leading noted in SS barrels is a function of the alloy make up or that it machines more smoothly. SS in all it's barrel alloy types does have more chrome in it than does CM steel. I wonder if the same is true if the CM barrels are carefully hand lapped?
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Re: BPCR Exterior Ballistics

Post by SSShooter »

Dan & Jim - thanks for the info. Do shoot that bullet, but only out to 300 (pigs & 300yd BPTR) thus far with 58gr of Swiss 2F. Has treated me well with a few pig pins, including Raton this past July. Need to "stoke it" with more powder and give it a run on the turkeys, rams, 600yd and longer.

Jim - what weight does that 38cal bullet cast at for you in 20-1?
Glenn
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Re: BPCR Exterior Ballistics

Post by DanTDesigns »

Don McDowell wrote:
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
Boy Howdy, is that part ever true, and surprising overlooked by many...
Lessons learned the hard way. :wink:
Don,

This bullet diagram brings to mind the solution to the under-stabilized bullet problems some were having when shooting way out yonder with their 19-twist, 44-cal Shilohs. Seems a certain business man now makes a mould like yours.

http://www.sageoutfitters.com/catalog/i ... 059926.htm

Image
All the best...DanT..."The nation which indulges towards another a habitual hatred or a habitual fondness is in some degree a slave.” - George Washington’s 1796 Farewell Address
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