Ballistic Coefficient vs. Accuracy?

[Distant Thunder]

Talking about loading for and shooting in Creedmoor matches, which do you think is most important, ballistic coefficient or accuracy? How much accuracy would you give up to have a higher B.C.?

Let's say you had two bullets, one that had B.C. of .380 and another bullet had a B.C. of .480. Bullet A and bullet B respectively. Bullet A with it's comparatively low B.C. will hold 1 to1 1/2 MOA at 800, 900 and 1000. Bullet B with it's higher B.C. will hold 2 to 2 1/2 MOA at those ranges.

Which bullet, A or B, would you choose?

I think we can all agree that accuracy is important. We can also agree that a higher B.C. is an advantage. Do you think a higher B.C. will overcome the less accuracy of bullet B? And vice versa, would the better accuracy of bullet A be enough to overcome its lower B.C.?

As an example of the differences in B.C. I'll use these two bullets, on the left is bullet A and on the right is bullet B. I'm using this picture because the difference in B.C. between the two is very evident. When in fact, these two bullets are equal in accuracy at 1000 yards in two tests during actual matches and shooting them at 1000 yards.

[beltfed]

I would definitely go with the bullet A.
As long as a person can wind dope well, to adjust for the
greater wind deflection of the lower BC bullet
Also, a high bc bullet (ogive) can be more tricky to dope is twitchy headwinds
Arnie

[Kurt]

Jim,

I will also choose #1. I have bullets with identical profiles like those two except my #1 is base poured and it does not have that .1" flat meplat.
#1 in the .45 and .44 caliber has kept me in the top 25 and 9th place at the Quigley shooting against 600 + shooters in some tough winds. I will choose the #1 profile over the #2 anytime and put a couple more twists on the elevation knob.

[Distant Thunder]

I know that we BPCR shooter work in a velocity range that all other shooting disciplines work hard to avoid as much as possible. The transonic velocity zone, from 1346 fps down to 897 fps, not only requires different bullet shapes than either supersonic or subsonic the requirements apparently change from the upper end to the lower end. Some compromises have to be made.

High power shooters just stay supersonic from the muzzle to the target, we can't do that with BP and lead bullets. Rimfire guys tend to start out at the lower end and transition to subsonic if the range is extended rather than go through the entire zone.

BPTR long-range shooters will mostly start out at the upper end of the transonic zone or somewhat about it and pretty much travel through the entire range. I have seen successful shooter with .45 caliber bullets in the 1250 fps range, but I found that I do much better when I start out near 1300 fps and up to about 1400 fps. I think most successful Creedmoor shooters are starting in the 1300 to 1400 fps range.

The two best bullet shapes for the transonic zone that are in use today are the elliptical and the money. I read recently that spinning these two shapes faster, using a faster twist, is helpful in maintaining stability through the transonic velocity zone. Also having the ogive of the bullet on the longer side can help but can get too long very easily and cause more trouble than it helps. Keeping some nose weight is considered a good thing.

All this gets complicated by how the conditions can push our bullets around, how much they are affected by windshear and quartering headwinds. Our bullets are deflected 3 times more than a .308 with a 155 grain Palma load. Our bullets are deflected a little less once they drop below 900 fps and are fully subsonic, but that's not until they reach 900 or so.

With a bullet starting out above the speed of sound the sonic wave is behind the bullet but quickly catches up to the bullet and as the bullet slows even more the sonic wave moves from the base to the tip of the bullet and eventually out in front of it. The effect of this sonic wave is what everybody else stays away from and we must learn to live with.

I think that if our bullets are designed to cope with the effects of the sonic wave and not so much to just be super slippery with a high B.C. we would be better served, and our scores would improve.

Of course, there is the possibility that the best bullet design might not be the most accurate in the rifle you have. I am not one of those shooters who builds a new rifle every year while chasing the next thing that will improve my scores. I have had some success tweaking the bullet design to get the best possible performance out of an existing rifle and very good accuracy seems to have followed along with that effort.

When I first designed my elliptical bullet, the bullet on the right in the picture above, I wasn't thinking of a high ballistic coefficient design I was just looking for a PPB that would be as accurate as possible in my rifle. The design started with Brent Danielson's prolate design and I modified it to work better in my 18-twist Shiloh .45-90. I doing so I actually gave up a good bit of the B.C. the prolate offers. How much I don't know.

As that bullet is today it has been a very accurate bullet for me and it has held up very well in conditions that other struggled in. I have no idea what the B.C. is and I don't care.

The bullet on the left in that picture is from a mold a friend of mine has and he uses it in his long-range muzzle loader. I only had about 50 of those bullets to work with so I didn't do any load development at all. I simply seated them on top of the same load I use for the elliptical in my .45-70.

I shot these two different times at to different rifle ranges at 1000 yards a couple of years ago. They shot just as accurately as my elliptical and I used the same sight setting as I do with my elliptical +/- one or two moa.

The results might be entirely different in tricky winds or other conditions, but I really couldn't see any difference in how they shot or the sight settings needed.

It's all very interesting what works and what doesn't in this sport and I wish I understood more of the whys and why nots of the transonic zone.

[mherth]

DT,
You’re making my hair hurt. With the bullet on the right there appears to be a very poor matchup of the patch edges. Is this of concern? I try to match the edges without any overlap or gaps, but as I grow tired I accept some of both. I wonder as I am patching how this affects accuracy. I also find patching DD bullets more frustrating than straight sided, but I’m getting better if I avoid hurrying. I’m sorry for not addressing you BC question, that is simply not something I wonder about. I have finally shot “some” 1.5 MOA with a DD bullet at 200 yards, but not consistently. 45-70. And when I went from shooting at 8” black bulls to 12” my scores improved with the same loads so far, or maybe I just had an unusually good day. I just glanced out the window and see snow coming down horizontally again…

[mherth]

DT, is the bullet on the left your Lodi bullet?
Kurt, which 45 caliber BACO mold comes closest to the bullet you favor?

[Distant Thunder]

Yea, I know Mike, nobody wants to talk about the transonic zone and what happens in there. It's like shooting into a blackhole, nobody knows what happens as the bullet passes thru and we all just hope our bullets come out the other side with good enough stability to still hit the target. I just can't help but wonder what's going in there! It's a question I can't answer but it won't go away either.

Whenever I post a picture of my PPB someone inevitably comments about my patching job. I don't know what to say, I'm working on it. I won't make any excuses for my patching and I'm not going to lie to you and tell most of my bullets look better than that. I don't get too excited about it, I do my best and I go and shoot. More often than not I do pretty well. Maybe I would win more matches if I did a better patching job. The truth is that picture is from a couple of years ago and I took it after the match so I would have a record of the two bullets I shot and how little difference there was between them on the 1000 yard target. I won that match, the Minnesota State Championship, shooting bullets that looked no better than the one on the right with the gap between the ends of the patch. I just don't worry about it very much.

I will note that I dry patch my bullets and they tend to unwrap if handled much outside the case as this one was during the picture taking and if you look closely you can see the patch is a bit loose which probably makes the gap look bigger than it really was.

It's kind of the same thing with the 2-D bullets. I don't get too worried about the little stuff. Some people cut special patches that are made to allow for the 2 diameters. I just cut regular patches and wrap a little cockeyed so that when the ends come around the leading edge is close, just close, to being in line. Doing it that way the gap is a little wider at the bottom than at the top, but what's a man to do. I load 'em up and go shoot. It all seems to work just fine.

Not sure what to say for you hurting hair! Mine hurts too when I can't answer the transonic question. Try not to lose any sleep over it, I lose enough for both of us!

[Distant Thunder]

Mike,

The bullet on the right is my Lodi bullet. Here's a better picture of it, naked and with less distortion due to camera angle. It's not a pretty bullet but the damn thing shoots really well for me. That mold has had more than a few surgeries to make adjustments to get it to perform better. It can be a bugger to cast good bullets with and once I get it to start making good ones I don't like to stop.

I have tried a few other bullets (molds), but none work as well as this one.

[Kurt]

It's a Paul Jones mould Jim

[mherth]

Jim, I am relieved at your response to patching. I am dry patching the DD bullets as you described and getting pretty consistent. I had thought about trying to trying to see if I could detect a difference between poorly or well wrapped patches on accuracy but decided to conserve what powder I have left. So one more variable to not be concerned about makes me happy!
Mike