Help Me Understand Boolit Design

[rodwha]

I greatly love casting and shooting my black powder arms. I want to hunt with these. Because of that I prefer a large meplat. However I'd like to create a universal boolit for both my pistols at short range and rifles for long range. For that a higher BC is good.

Were I to have the same OAL but change from a wide meplat to a more aerodynamic nose with all else being the same how much would it effect the BC? To make this easier let's compare a SWC to an almost pointy bullet with a small flat meplat. Let's say the SWC version weighs 230 grns (.45 cal). I assume the pointier boolit would weigh about 15-20 grns less. Is there a big enough impact on the BC out to 125 yds? Or is it minimal making a wider meplat more ideal? Does the extra mass make up for the loss of aerodynamics?

[Wayne Smith]

I think, but it's been years since I've done it, that Don's Mountain Molds design program provices estimated BC. If it does you can design a boolit and change any parameter and see what it does. Very nice program.

You also need to think about the typical ranges at which you hunt. If you are typically under 200yds changing the BC makes very little difference in the point of impact of the boolit.

[rodwha]

Thanks!

For handgun hunting 25 yds or so would likely be max. I have my eye on a Remington revolving carbine though. As this can generate around 600 ft/lbs at the muzzle according to a fellow who has one and has tested it with the same powder and similar boolits and so this can actually be used rather far (100 yds?). I also want either an additional barrel for my rifle or one specifically for hunting fields topped with a Malcolm style scope. 200 yds may be doable if the BC is rather high. I kind of doubt I could stretch it that far though with the way I think I'd prefer it set up (under 5" high/low).

[rodwha]

I fiddled with it a bit but didn't see an estimated BC. But I may have not figured out how to work it.

[Grump]

From the days when I pored over paper ballistics tables for way too much time, I remember that .35 caliber bullets with 600 foot-pound of energy dropped a lot and lost a huge amount of steam between 100 and 200 yards. My conclusion was that 100 really was the limit for that caliber.

And larger calibers dropped about the same but could retain more reasonable amounts of energy only because they started out with more. BCs were not that different as I recall.

BUT that was always with low-BC revolver bullets. .15 ish to the .18 or so on the G1 model... but I was comparing .357s with .44 Mags...then I noticed the .41 Mag bullets were "all the way up" into the low .2 BCs.

Haven't yet looked up how much a truly pointy boolit would help. Still need to run my .30 Carbine 100-300 yard experiment with pointy 110-gr JHPs. They work just fine and safely reach the same velocities as the traditional RN types.

[rodwha]

I'm curious what you are working with with the .30 Carb. My old boss had a Ruger Blackhawk in .30 Carb. We talked a bit about commercial loads for hunting. I told him he'd be better off reloading for that most likely. I hated shooting that gun more than anything else! That crack it had when you pulled the trigger...

[17nut]

BC gets more important and of a higher value as speed goes up.
Take typical Sierra bullet and they list 3 different BC's according to speed.

When you pass below speed of sound bc is less critical.
Impact is important at low speeds and that is why a flatnose bullet "kills" better than a round nose bullet wich just zips through the animal.
Veral Smith said that optimum speed when an animal is hit is in the range of 1400-1700fps (for flat nose bullets). That gives the best ballance between meat disruption/shick and penetration.

Here is some exambles of a 45 cal 230gr bullet going 900fps:

BC = .2 (full wadcutter territory)
Speed 100: 835fps
Speed 200: 775fps

BC = .3
Speed 100: 856fps
Speed 200: 815fps

BC = .4
Speed 100: 867fps
Speed 200: 835fps

BC = .5 (good pointy bullet)
Speed 100: 873fps
Speed 200: 848fps

See? BC isnt as critical as you might think at low speeds.

[Bigslug]

It sounds like you're planing to hunt with antiques or replicas, so you should probably also factor bullet stability into your plans. If your barrel is a slow twist intended for round balls, you might not be able to get away with making them terribly long and pointy. Also. . .Remington revolving carbine. . .rammer will be contoured for round ball.

Otherwise, it sounds like you're looking for something like Keith SWC's or the more modern equivalent LFN that run with a meplat somewhere between 65% and 70% of the total bullet diameter. The the accuracy of WFN formats pushing 75% meplats tends to come unglued farther out. I'm presently playing with a 420 grain .45-70 with a .34"/75% nose. With a launch speed of just under 1400fps, it groups wonderfully at 150 yards, but presents a 15" buckshot pattern at 200. It's pretty commonly known that a 100% meplat (full wadcutter) .38 at slow, match velocities is wonderfully accurate to the NRA Bullseye distance of 50 yards looses that characteristic soon after punching paper. The hammer noses are great inside their stability range, while the Keith/LFN is going to be your ideal compromise between ability to shoot at distance and blunt force trauma. Both good. . .provided they stabilize in your bore to begin with. Berger has an online twist rate stability calculator that can help you figure that out.

As to trajectory. . .NOE lists approximate BC's for their molds that I've found to track pretty accurately. Accurate Molds gives detailed blueprints of theirs that could be compared to something similar from NOE to get you in the ballpark. Plugging your variables into Hornady's online ballistic calculator will rapidly start to tell you what is and isn't possible.

[rodwha]

Indeed I am intending on hunting with reproductions.

My revolvers are both faster twists around 1:16". My .50 cal rifle is 1:48". I have no idea what the revolving carbine has and intend on another .50 cal in either 1:48 or 1:32".

I went to Accurate to make me a 195 grn WFN thinking my Remington pistol would be a much slower 1:30" twist but found that not to be the case (2013 model). Not knowing the specifics on wide meplats I had him give me a .375" (83%) nose.

Currently I'm considering a 75% (.340") nose.

[BAGTIC]

Perhaps these free online computer programs can help you.


http://www.geoffrey-kolbe.com/drag.htm

http://www.geoffrey-kolbe.com/external_ballistics.htm

[BAGTIC]

There is NO SUCH THING as a UNIVERSAL BULLET.

Flat trajectory at long range demands high velocity and high sectional density. Handgun and carbines are not going to provide those combinations. Handgun cartridges are designed with very limited ogive lengths that will severely increase drag when pushed to high velocities, Velocities below M 1.3 are usually most efficient (lowest drag) with round nose bullets. Above that spitzers reign. How man handgun cartridges will accept long ogive bullets. An example of this is that for extended range ballistics the case of the .44 Magnum is too long. If its case length had been kept at .44 S&W length or shorter the increased available length for a longer ogive would have made it more efficient. Even if it had started at a little less velocity and recoil it would have retained as much or more velocity, energy, and momentum 'way out there'.

Looking at the old black powder big bores used for long range shooting they almost all used the RN bullet design which was not a handicap to them because the black powder loads kept their velocities in the below M 1.3 velocity range anyway. There was no way to flatten trajectory in that velocity parameter except to increase bullet weight and therefore sectional density as effective B.C. increases proportional to S.D..

[rodwha]

Thanks! I'll check that out.

By universal I meant a compromise so as to work ok in each situation.

I also have a short for weight 285 grn WFN I've considered trying in a sabot. It drops at 0.456" though. I'm not sure if it would work in a .458/.50 sabot. Otherwise I'd need to size it. However it also has the .375" (83%) meplat.

Does 1.3 M stand for Mach? My understanding is this velocity is somewhere around 1100 fps, right?

[Bigslug]

A little hard to interpret exactly what you're loading for, but if you're looking for a short, fat, .45 caliber pistol bullet to load in either a handgun or saboted in a larger bore, you could go with the Keith 452423 - a 240-ish grain bullet for the .45 Auto Rim, which gives you the 75% meplat in a package that might stabilize in a slower twist, but might have trouble reaching the longer distances.

Somewhat longer/heavier is the Keith 454424 which ups the weight to 255 grains drops the meplat down to .32", and gains a much better reputation for distance.

There's also the RCBS SAA bullet that, as best I can tell, is merely the 454424 stretched a little to bring the weight up to the 270 grain ballpark.

NOE makes clones of all three, and lists dimensions and approximate BC's. Should be able to figure out the necessary spins and speeds easily enough. Might save you needing to go the custom route.

[rodwha]

Very much what I'm looking into, but for black powder percussion guns. These need to be slightly over chamber size and require a rebated base to slip into the chamber to ensure it loads straight.

Custom is the way I have to go as I don't care much for the commercial versions available. And I like being able to create precisely what I (think) want.

As I am dealing with a specific volume and length and found that my accurate powder charge didn't change despite projectile differences I figured I'd try to fill the excess with boolit.