Kansas Cast Boolit Cadre Strikes Again

[fourarmed]

The weather is usually a factor at the March Silhouette match. This time we had about every type there is. We started the day with a microburst that tore up trees and buildings over a large area, and followed that with tornadoes, hail, and torrential rain accompanied by thunder and lightning, and interspersed with moments of uneasy quiet and strange light. Toward the end of the day, I went out to give a hand to one of the young target setters. He was standing stoically under the only spot in the bunker roof that didn't leak – much. He was amazingly cheerful about the whole thing. Said he just hoped the sun didn't come out and make it muggy. Of course, five minutes later, it did.

None of this held back JSH. He shot a UAS 40, and then cleaned all 10 200m. shootoff chickens. He was using a scoped Contender in .30-30. Yers Truly started the season with a standing 30. Had to get 8x10 rams to do it. I was shooting the SAECO .270 borerider Beagled a thousandth. This was in an ISGW-sighted Merrill .270 maximum with 15 gr. of 4759. I used WDWW at 50 and 100, straight linotype at 150 and 200.

[Beerd]

Excellent shooting.
I used ta shoot straight lino in a 30 Herrett, 160 grain at about 1600 ft/sec, but lost 50% of center hit pigs. I figgured the boolits were too brittle and were shattering on the targets. Is that why you use wheel weights?
..

[fourarmed]

Beerd, I can't imagine why your load would ring pigs. It is slightly more powerful than mine (130 gr. at 1700). I use the WW at 50 and 100 to conserve linotype. I use the Lino at 150 and 200 because it's a little more accurate. There just is no scientific reason why Linotype would have less momentum transfer to a silhouette than a softer alloy. It would produce a slightly lighter bullet, but the difference is not great. I have heard that claim made by others, but I don't believe that the alloy is the reason. Were the pigs and stands at your range of standard construction?

[Scrounger]

A brittle bullet dissipates a lot of energy in blowing up, therefore less is transferred to the target. I too found softer worked better...

[fourarmed]

Scrounger, this topic is often a source of heated debate, but the physics is pretty simple. The operative principle in any collision is: The total momentum of the system (pig and bullet) is the same after the collision as before. It doesn't matter what the bullet is made of, or whether it blows up or not (and they all do).

This is not true of kinetic energy. In fact, only a very small amount- on the order of 1% - of the bullet's KE is passed to the silhouette under any circumstances. Most of it winds up as heat.

If Beerd was hitting those pigs with a load like he described, and they were not going down, it had little or nothing to do with the alloy. If a pig's feet and the stands are muddy, or even wet, they are much harder to knock down - especially if you hit them in the center or lower. Wind can be a big factor as well. I would also be willing to bet that if his load had been chronographed that day, he would have found it was not as powerful as he thought it was out at 100 yards.

I'm not setting myself up as an expert here, but I know basic physics and I have knocked over a hell of a lot of silhouettes (and rang a few) in the last 20 years. If you are interested in a more technical discussion, one went on (and on, and on) over on the IHMSA board a while back. I could probably find the URL if you would like to look at it.

[fourarmed]

I thought about this overnight. I know a lot of people believe with Beerd and Scrounger that linotype boolits don't have the knockdown effect on metallic silhouettes that softer boolits do. I believe that the real reason is this: Cast from the same mold, a lino boolit is going to be lighter than - say - a WW bullet. As a result, when loaded to about the same muzzle velocity, it is going to lose more of that velocity to air resistance than the softer/heavier boolit. Consequently, the lino boolit gets to the target with less mass and less velocity, ergo less momentum.

Since small diameter (under .30) cast boolit loads out of pistol barrels aren't carrying a huge amount of momentum anyway, the lino load is going to be more marginal than the WW load. But it has nothing to do with the hardness per se. If the two were loaded so as to produce the same momentum AT THE TARGET, there would be no measurable difference in the knockdown effect.

[KTN]

I´m no expert on silhouette shooting,but here´s one story about silhouette bullets.Back in the 80´s,Lapua made .357" 180gr solid copper silhouette bullet called Tera.Idea was,that bullet won´t shatter on impact,but it will flatten on target,pushing it a bit longer.What I heard from silhouette shooters,bullet worked really well,it didn´t shatter and it knocked targets down well.But there was other problems,being made of soft copper,it fouled barrels,and being solid copper,it was long compared to it´s weight,so if you were using it in revolver,it took up case volume.There must be some reason every manufacturer makes their silhouette bullets thick jacketed and hard,so they don´t shatter on impact.


Kaj

[fourarmed]

Probably so they would sell better, is my guess.

Seriously, the 180 and 200 grain .357 silhouette bullets that were put on the market when the .357 Maximum revolvers came out did knock silhouettes down better, but it wasn't because of their construction. The additional bullet weight retained downrange momentum better . A 158 grain .357 bullet sheds velocity like a duck sheds water. They are seeing some use again in the .357 mag Freedom Arms revolvers because they leave more powder room (as you stated) and because the FA guns are strong enough to jack up the muzzle velocity to offset the losses.

Long experience by a lot of steel shooters indicates you need pretty close to 1 pound second of momentum to knock the rams down reliably. That is a 180 grainer at about 1240 (at the target) or a 158 at a little over 1400 (at the target). Either one of those is going to strain most revolvers. People using guns that can't safely produce that much downrange momentum try all sorts of voodoo to make up the shortfall. If they want to spend their money on voodoo, that's their business. I'll spend mine on momentum.

[slughammer]

Since small diameter (under .30) cast boolit loads out of pistol barrels aren't carrying a huge amount of momentum anyway, the lino load is going to be more marginal than the WW load. But it has nothing to do with the hardness per se. If the two were loaded so as to produce the same momentum AT THE TARGET, there would be no measurable difference in the knockdown effect.

Each year I shoot the PSA shootout, its a knockdown steel plate event for time. Most of the targets are engaged at 15 to 25 yards. I've seen lots of 115gr jacketed at 1100FPS fail to take down the larger targets, while 150gr lead at 840 FPS reliably take them down.

I think the physics of knocking down steel targets is closer to an "Impulse" (IIRC) which is based on Force x Time. The longer boolit going slower is in contact with the steel for a longer period of time and therefore it is able to transfer a better Impulse to the target. And on the same idea, if a boolit is able to hold together longer it will be in contact longer and thus impart more enerygy.

One year early on I showed up with a 95gr boolit going 1350 FPS, I had to shoot the big ones in the head to take them down.

[7br]

Resources used:Velocity calculations: http://www.handloads.com/calc/
Momentum = wt in grains * velocity in fps / 225000

Here are the numbers.
BC of the 150gr bullet is about .148. The 115 jhp is about .114 and the 95gr jhp is .09.

BULLET ******15 yards********25 yards
150gr------------ 828fps:.552 ------ 821fps:.547
115 jhp --------- 1060fps:.541 ----- 1038fps:.530
95jhp ----------- 1263fps:.533 ------ 1215fps:.513

I think I will stick with forearmed on this one.

Actually, all of the momentum and energy has to be accounted for.

[fourarmed]

Slughammer, you are right about impulse. However, impulse (F*t) equals change in momentum, which is what I have been saying all along. The time factor alone is a blind alley, and here's why: Suppose two bullets hit the target with the same momentum, but one is in contact with the target for .02 milliseconds and the other for .01 milliseconds - half as much. Both undergo the same momentum change, so the one with twice the contact time exerts half as much Force. F*t is the same for both.

Mark's point about ballistic coefficient is particularly germane. The loads you mention have about the same momentum at the muzzle, but downrange the advantage quickly shifts to the one that has the best BC. For similar shaped bullets, sectional density has the same effect. This goes back to the business about linotype versus denser alloys.

[slughammer]

The loads I mention are only traveling 15-25 yards. So downrange loss is negligable. I don't think both boolits in your example undergo the same momentum change. Only if they don't blow up and they just stick to the target, then it is like physics and the "collision" mentioned before. But they do blow up and still have energy to spend on the surrounding terrain.

It is actually a coinsidence how close those loads are for mass x velocity. I'm only estimating what a factory jacketed 9mm 115gr load does out of a full size Beretta, but I think 1100 is close. The other 2 loads were ones that I have used and chronoed. Just my observations based on several years of shooting this match, seeing the strikes and standing there. All of the boolits energy is not transfered to the target, lots of it remains as the boolit splatters and the bits go flying. My observations are just telling me that taking them down vs. not taking them down; has a bunch to do with how well the boolit holds together, sticks to the target, imparts just some of its energy and then expends the rest blowing up.

The 95 gr boolit from years ago was Lyman 358242.
My current practice boolit is the Lee 125-2R, drops at 130gr, .358 and 4.5 of AmSel chronos at 926fps.
Too much entry fee and prize money on the line for me to chance it with a the 130. I just finished loading some of Roger's Better Bullets, 148gr cast, 3.9 WST is good for 840 FPS. Wish me luck...

[fourarmed]

Good luck is definitely in order. Having shot a little of that kind of steel, too, I know that there isn't anything you can safely put through a 9mm or .38 spl. that is going to be 100% on plates and poppers.

You are right that the difference in momentum at the muzzle and 15 to 25 yards is minimal, but what difference there is does favor bullet weight, as 7BR's calculations clearly show. More relevant is that if two different loads have the same kinetic energy, the heavier bullet will have more momentum by a factor equal to the ratio of the velocities. It's not mere whimsy that the silhouette battle cry is "More powder, bigger bullets."

Your statement that the fragmentation of the bullet makes a difference in momentum transfer is not correct. It makes utterly no difference whether the bullet sticks to the target in a lump or shatters and throws all its shrapnel sideways. I know it sounds strange, but an Oreo cookie would knock down a silhouette if it were going fast enough to have the needed momentum.

Now, if some of the shrapnel bounces backwards, that does increase the momentum delivered to the target. This leaves a teensy bit of wiggle room for the people who believe bullet construction matters. My calculations and observations indicate that backsplash momentum is too small for any differences between brands or types of bullets to be significant.

I just learned that Hornady did some experiments on this back in the early days of silhouette, and published the results in American Rifleman. My informant says that – presuming the bullet doesn't crater the target – they found no difference due to bullet construction. I have requested a copy of the article, and will be happy to pass it along if anyone would like to see it.

[JSH]

Bob, if you get a chance I would be interested in the reading material.
I still have to chuckle about the FMJ thread you refered to above. One of the questions is, why the silhouette shooters used them. I still have to stick to my guns as the answer being 99.9% was the cost per bullet. The supposed knock down power was only second and that was a "guesstimate" by most at best.
Jeff

[fourarmed]

Jeff, I have the article. I will get your email from Margaret and send it along. It is very informative. Turns out that the backsplash momentum of a shattering bullet increases the momentum of the target about 11% above the striking momentum of the bullet on average. A bullet tough enough to remain in one piece and stick in the target - which a lot of guys think would increase knockdown - would actually decrease it, because the target would get only the striking momentum of the bullet in that case.

The only bullet which showed a slightly significant increase in momentum transfer was the 55 gr. .224 spire point (about 16% backsplash), and the experimenters said that by the time they tried it, the steel surface of the ballistic pendulum was getting roughened. That of course increases backsplash. The only bullets that showed significantly less backsplash (about 7%) were the 100 gr. .243 spire point, and the 100 gr. 9mm FMJ-RN. Presumably all the bullets tested were Hornady, which would mean that the lead bullets tested were swaged.