critique bullet design, long range 45 cal

[Whiterabbit]

Hi guys,

I upped another thread, I think it wont get the exposure I would get by putting it in the proper place with its own thread.

I drew up a couple examples, and I am interested in everyone's opinion with respect to GEBERAL bullet design factors to make a bullet accurate.

I chatted with Runfiverun awhile and got some great tips. I incorporated those into the design here and would love more input.

It's supposed to be a 45 cal, but I only have access to mountain molds site besides drawing on paper. Therefore, to use the site I had to scale everything down 75%. For any given dimension, the real number can be had by dividing by .75. More often, it seems that good bullet design relies of ratios rather than values (driving band vs nose, band width vs lube groove ratio, etc.) The actual weight ends up being around 750 grains. Interested in folks thoughts. On the nitty gritty design, not on the merits of such a heavy bullet or whether it will work for the firearm or not (in concept, it will).

same bullet, just with and without crimp groove (I don't need to crimp, and will technically not be using the crimp groove)

http://castboolits.gunloads.com/attachment.php?attachmentid=71355&d=1369328344

http://castboolits.gunloads.com/attachment.php?attachmentid=71354&d=1369328341

highlights:
60%/40% body to nose
big driving band in the front and back
30% of the nose is bore ride
.2" meplat (accurate molds friendly)
bore ride is to be tapered from bore ride diameter up to body diameter
wide shallow lube grooves (copy old west bullet mold design)
any actual dimension wanted, just divide the number by .75

critiques? any of you guys see any "gotchas"?

(I did not anticipate how much fun bullet design is.)

[Whiterabbit]

as an fyi, mt molds site says the nose is unsupported (too long), but it is counting the front drive band as unsupported nose, even though it is full body diameter. So the reality is the nose is shorter than the mt molds website thinks.

[runfiverun]

nobody?
not even a looks good, or an ewww no way.
or it weighs what?

[Whiterabbit]

I kinda like the crimp groove model better. I could ask for the crimp groove removed, which would give me a HUGE front driving band. That would allow me a large area to play with OAL while fully enclosing the grease grooves. The first option goes from deep seated to seated long but barely covering the first grease groove to fully exposing it.

i keep my ammo in MTM boxes, but it would still be nice to have all the grease in the case.

[Buckshot]

............I've fired a 560gr slug:

http://www.fototime.com/4C9F502AC298773/standard.jpg

from my Rigby MLing match rifle (hadn't been PP'd yet) over 85.0grs of Swiss 2Fg a few times and it was more fun then I could stand. But 750 grs? Isn't the std weight for a 50 BMG something like 650grs?

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

[Oreo]

nobody?
not even a looks good, or an ewww no way.
or it weighs what?

Ok, I'll play...

750gr! Dam. Just dam.

In terms of the bullet design nitty-gritty, you should calculate the position of the center of mass as well as the center of cross-sectional area. Really you only need to know the lengthwise positions of each. There was a good post in another thread recently that explained the importance and where they should be located.

ETA: Found it. Here ya go, read this and apply what you learn:
http://castboolits.gunloads.com/showthread.php?t=198936

[Whiterabbit]

Thank you Oreo.

[Whiterabbit]

I'm kind of thinking the lower bullet, with the crimp groove deleted. It has the same lube capacity of a 500 grain bullet and the massive front driving band lets me seat deep or seat out.

The nose isn't too far off BPCR type designs.

Balancing CG and CP isn't easily done in this case because we are talking about a bullet for longer ranges (possibly), where BC might play a role. There's a reason boat tails and streamlined bullets are used for long range even though they have a destabilizing discrepancy between CG and CP. so IMO it is a non issue for this design.

[MtGun44]

What twist rate will you need to stabilize that spear?

Bill

[Whiterabbit]

theoretically 1 in 16. Technically, I've only tried bullets up to 1.6 inches long. This will clock in at 1.925, which is what math and the internet tell me is the ideal length bullet for the twist rate. the gun will take a 2.125 (give or take) long bullet physically, and the 1.6"-er (740 grains) shot best WAY below max pressure, so I;ve got some headroom to push harder, assuming an accuracy node is available.

Just wanna make sure the bullet is as capable as possible to do a many different things. A mold is an investment sure, but the bigger investment is the reality of pouring nine bullets per pound of lead.

[NVScouter]

I'd worry that the lube grooves are too narrow. Not for capacity but the back pressure may cause the bands to distort more than usual. What MV are you shooting for?

[Whiterabbit]

What MV are you shooting for?

shooting for? 900 fps in gun #1, honestly. But I have a feeling I'll find the accuracy node lower than that.

That being said, I do recognize that longer bullets need more velocity in the same twist to stabilize. And that I haven't chronoed my 740's yet, but know they are slow. So if I have to push these hard to get them to stabilize, then at least I am using the gun to its full pressure potential.

The honest truth is that for the first gun, these are gonna be used at 100 yards max. Maybe 125-150 on a blue moon one time. But I don't want to commit to a standard shotgun or pistol type bullet design because I have those designs that work. I want something that could work as a long range design so maybe there is gun #2 down the line that I can push these much harder and try to get some yardage out of them.

Thus the interest in bpcr kinds of design details for integration.

I CAN use design #1 with the wide lube grooves. They will have WAY more lube capacity than a 500-600 grain BPCR 45 cal bullet. It's just that if I seat the bullet out the upper lube groove will be exposed. Which is OK, I store my ammo in MTM boxes. But still wouldn't mind covering everything up.

[Whiterabbit]

I'd worry that the lube grooves are too narrow. Not for capacity but the back pressure may cause the bands to distort more than usual.

What do you mean by narrow, by the way? Do you mean the length? Do you mean the grooves are "too deep" so the bullet diameter in the groove is too small?

I may have to agree with you. I did not specify groove depth (no input for it). I did notice the Old West lead zeppelin has VERY shallow grooves that are very very wide. The Hoch goes for a different approach, more traditional depth and many numbered lube grooves.

Seems to work both ways? I might be shooting them too slow to see a difference, but they both shoot well in my gun. (the 540 grain Hoch, and the 590 grain lead zeppelin)

[btroj]

Hope you have a really big casting pot. Those are gonna empty it FAST

[Whiterabbit]

Understood. I have a plinker bullet, a 460-425 6-cav ranchdog mold. Might re-try the lee 300 grain, though I have to shoot those so slow it may not be worth it.

[runfiverun]

I think I like the bottom boolit better mainly for the lube grooves.
the crimp groove would also allow some metal displacement from the front drive band.
you don't need to fill all the lube grooves in fact you could get by with just the bottom one.

[Whiterabbit]

gosh, so lube capacity is of no concern to you? Also, why is metal displacement of the front band a concern? Honest question, my CA-approved hunting bullet for this gun is a barnes 290 grain solid copper bullet which has NO driving bands a all. Just smooth solid copper for miles.

[Liberty'sSon]

I don't have the experience to add much, but I can say that is one BAB, Big &$$ Bullet.

[runfiverun]

lube capacity isn't that big a deal to me unless you need it to keep powder fouling soft.
you can manipulate a small amount of lube to leave behind a good even barrel coating without fear of purging.

[Whiterabbit]

cool. Sounds like nary a peep on the nose design too, so that must be less critical to the process. Sounds like I'm good to go. Now's all I need is money.