Bullet balance and BPCR's

[Blackwater]

I keep playing with Dan's bullet design program, trying to finalize on a bullet mould for my BPCR Browning. Gotta' question;

For BPCR's specifically, and others generally, do I want the bullet's center of gravity, or its balance point, behind the mid-point in its length? Does this contribute to a bullet's stability in flight, and how important a criteria have you found it to be? Why does this make a difference, and is this a particularly significant factor in BPCR bullets because of its early entry into the transonic range?

I ask this because I remember reading some article about balance in Sierra Matchkings, I believe it was (maybe just used as an example?), but can't remember the specifics. Looks like my CRS disease is getting stronger every day! Dang it's hard when you get to a point you remember just enough to get yourself confused!

[Bass Ackward]

For BPCR's specifically, and others generally, do I want the bullet's center of gravity, or its balance point, behind the mid-point in its length? Does this contribute to a bullet's stability in flight, and how important a criteria have you found it to be? Why does this make a difference, and is this a particularly significant factor in BPCR bullets because of its early entry into the transonic range?

Dennis,

This is probably the least understood factor to cast. The more weight you can keep on the back the easier a bullet is to stabilize. The theory to the bore ride bullet. But for the strongest design, you want as much bearing area as possible.

Keith took this to heart with the semi wadcutter design which cuts nose weight. So when the bullet passes back through the barrier, it has the best chance to remain stabilized. This also was the theory to the trunicated cone design. Cut as much nose weight as possible or have the most bearing length as possible or put the balance on the back of the bullet.

I hold to an 80 / 20 rule now for "my" cast designs now. Besides the barrier, this also helps with bullets that are outta balance a little. Whether the outta balance is caused by a defect in the molding process. Or the sizing process which also incluses the sizing of the throat / bore. Or even the shooting process where the bullet obturates in an uneven fashion or encounters bore fouling which often settles in the 6 o'clock position because of gravity. When I adhere to this ratio, fliers go less wild. And as a result accuracy improves over all. This matters to me because I count the fliers in a group as well. The more unsupported nose weight you have or the better the ballistic coefficient, the more perfect the conditions have to be to stabilize it perfectly.

The down side to the 80 / 20 formula is that meplat size must be sacrificed in order to maintain ballistic coefficient. Or just accept a shorter range bullet what ever that might be. But state it as you choose, the less unsupported nose weight you have, the longer your bearing length will be and the stronger the bullet design you will have to compensate for whatever. IMO

[45 2.1]

Do I want the bullet's center of gravity, or its balance point, behind the mid-point in its length?

It will be unless your shooting a wadcutter.

But for the strongest design, you want as much bearing area as possible.

You can have too long of bearing. Just what are you doing here, hunting or long range target. If hunting, pick something with about 1.75 caliber bearing length with a nose thats a short FN . If target, then get a 500 to 550 gr. with 1.75 to 2 calibers of bearing a a long RN that will grate on the fouling when you chamber it. Either bullet needs alot of lube groove capacity.

[Buckshot]

............Take a look at the Lyman Postell or the Saeco #745 for a couple good boolit designs to work from (or just use THEM ). Also the Lyman copy of the 500 gr Gov't slug flew point on from an 18" twist barrel to 3800 yards during the Sandy Hook, NJ trials. All 3 are well balanced designs for BPCR use.

..................Buckshot

[Blackwater]

Thanks, guys. And for .45 2.1, when I read your comment about the wadcutter, I just went "Duh!" Couldn't help but chuckle. And also, the designs I've been thinking I'm sorta' satisfied with tend to almost uniformly wind up carrying a capacity of @ 1.6 gr. of lube. That should be aplenty, shouldn't it? Any advantage to using fewer, larger grooves? I keep thinking 3 lube grooves looks about right, with 1:1 groove/band ratios. My Browning has shown no problems with that Saeco #745 of mine using Emmert's with @ 6% lanolin added. Blow tubing keeps the fouling soft, wet and soapy. Cleanup is generally with one wet patch and one dry one, though I always use more just to be sure.

I've wrung this Saeco bullet out fairly well, I think, and I think it's time to move on and try another bullet. I really like Dan's moulds - aluminum with the 304 SS alignment pins. Very nice moulds. I may be a bit like the moth to the flame right now, but can't resist trying one of his moulds next. For $60 for a single cavity, he just can't be beat. Nice guy, too, and I like dealing with folks like that, and particularly if they're also real shooters.

Just too many things making me want to try my own design. At worst, maybe I'll learn something. Still think I want to try a bore rider, though I've been warned, so I can get more powder in that 2.1" case. At worst, maybe I can sell those beautiful moulds if they don't work in my gun. Being a hunter, I also keep flirting with a 60% nose when I know a smaller meplat will help it down range.

Compromise hasn't ever been my strongest suit. I also plan on trying that new Lee BP design. A couple of buddies have gotten really good results from it, and the price of the mould is just too good NOT to try it.

Really great to have such strong knowledge and experience here, even if I do go off like that candlefly now and then. After all, this IS an adventure, right?

[45 2.1]

If your going to shoot blackpowder, more lube is better than less lube. You are having to blow tube, aren't you. The best bullet in terms of lube capacity seems to be the LEE 459-405-HB. Still, I would want more lube than that, maybe with more, you wouldn't have to blow tube AT ALL. Just look at Pidgeon roost Slims big groove bullets and their excellent reputation.

[Ben_51004]

I have a Browning BPCR in .45-70 (also one in .45-65, but that's another story). I found mine to be pretty accurate with the Lyman 457132 (Postell), RCBS 45-500-BPCS amd the Lee 459-405-HB. On my rifle the type of powder, weight, and drop technuques seemed to be more critical once a proper bullet was selected. I tried Elephant, Goex, Swiss, and also the BP substitutes (not satisfactory), and a couple different lubes.
What I finally settled on was the Lyman bullet, 18" drop tube, homemade lube and GOEX powder. The Swiss would probably be more accurate but it was more expensive, harder to find and the Goex was shooting as well as I could hold. The Lee was very accurate and useable at short range (chickens). I also found that 100 yard testing was good for a general idea of accuracy, but 200 yard testing was necessary for final load development. Very interesting, those black powder rifles!! (Ever hear of a bullet going to "sleep?")
I found that I was obsessing about bullets, but finally realized I was trying to re-invent the wheel, so to speak. All this work had already been done; all I had to do was find the information. I did get some really good advice from several extrememly knowledgeable people that helped me on my way and saved me a TON of time, money and worry.
I suggest that for some good recipes for your rifle, talk to Ernie Stallman of Badger Barrels (he made the barrel on your rifle), and also the good folks at Buffalo Arms.
I used to shoot at the St. Louis rifle and shotgun club; had a LOT of fun there shooting, and even won a little. Great folks. You don't need to spend a lot of time and money making these rifles shoot, but you can if you want to! Good luck!! ~Ben~