Any formulae for predicting efficacy?

[Pond James Pond]

If you know the diameter of your bullet, its weight and its velocity are there any methods of predicting, within reason, likely penetration from a SD point of view.

It is the age old issue of round choice and I have two options that I have simply because they are available and others are not: both 158gr, both manage about 800fps/250ftlb at the muzzle (adjusted to snub performance), both have a flat nose.
One is FMJ, the other SP.

I have touched on this issue in the past and got various responses mostly pointing to the flattest, widest meplat possible and so far these two rounds are it, aside from WC although those are pretty weak loads with 670fps and 150ftlb at the muzzle (also adjusted to snub performance).

I want to know if the SPs would yield any worthwhile expansion and if, in doing so, would it still retain any decent penetration.

I do not want to start a calibre war as it would serve , and I'd like to avoid multiple cartridge suggestions by just sticking to those mentioned above and the question below.

My one and only question is if there is a way of approximating, on paper, how a given round might perform in an SD situation given the parameters I have avaialble.

 

[Theohazard]

There's no good way to accurately predict how any given round will perform in an SD situation simply because there are just too many variables involved: The target's multiple layers of clothing; their body type; what angle it hits; where on the body it hits; how much muscle, fat, or bone it hits; etc.

The best we can do is test specific rounds in simulations (like ballistics gel), or measure real-world performance of those rounds and try to get a general average. In terms of predicting performance, it's much easier to just compare the two: I can be fairly sure that -- if all else is equal -- a flat-nose FMJ will penetrate more and expand less than a flat-nose soft-point. But it probably won't make much difference; I doubt the soft-point will expand much at all given the low velocity, but with a 158 gr. projectile at 800 FPS (I assume you're talking about a .38 Spl here?), I think it will probably tend to penetrate the FBI minimum 12" most of the time.

 

[481]

My one and only question is if there is a way of approximating, on paper, how a given round might perform in an SD situation given the parameters I have avaialble.

You can use either, or both, of the mathematical bullet penetration models proposed by Charles Schwartz:

and/or Duncan MacPherson:

to do that.

If you know the diameter of your bullet, its weight and its velocity are there any methods of predicting, within reason, likely penetration from a SD point of view.

You will have to shoot the SP into water to get an average expanded diameter and retained weight, but that is not necessary for the FMJ since it won't expand under those conditions. After that, all that is required is to just plug in your data to either model and you'll have a pretty decent prediction of what each round is capable of.

 

[Pond James Pond]

Thanks to both of you and, yes, this is .38Spl.

The water test would be interesting. Not the least being trying to convince my outdoor range to let me!!

 

[Jim Watson]

It takes a well designed hollowpoint to expand at .38 Special velocity.
I would not expect much if any from a JSP.

 

[481]

Thanks to both of you and, yes, this is .38Spl.

The water test would be interesting. Not the least being trying to convince my outdoor range to let me!!

Well, I can get you started on the .38 Special 158 gr. FMJFN @ 800 fps-

The Schwartz bullet penetration formula says that a .38 Special 158 gr. FMJFN @ 800 fps would penetrate to a depth of 74.75cm (that's about 29.4 inches) and permanently crush 33.16 grams of soft tissue. The MacPherson bullet penetration formula says it would penetrate to a depth of 77.72cm (that's about 30.6 inches) and permanently crush 34.36 grams of soft tissue. The formulas seem to agree with one another.

You'll have to do the soft-point bullet test yourself.

If your .38 Special soft-point fails to expand, it'll behave like the FMJFN and penetrate to the same depth (and crush the same amount of soft tissue) that the .38 158 gr. FMJFN does.

 

[Hal]

My one and only question is if there is a way of approximating, on paper, how a given round might perform in an SD situation given the parameters I have avaialble.

No - not really.

There's one potential wild card that's going to screw things all up.

Controlled expansion.

A bullet's cross sectional density is what mostly determines how deeply a bullet will penetrate.
As the nose expands, that sectional density figure changes.

Shooting into water will give you an idea of how much expansion might take place, but, it won't really tell you what the expansion was at what depth.

High speed cameras and ballistic gel are needed for that.

 

[481]

No - not really.

There's one potential wild card that's going to screw things all up.

Controlled expansion.

A bullet's cross sectional density is what mostly determines how deeply a bullet will penetrate.
As the nose expands, that sectional density figure changes.

Shooting into water will give you an idea of how much expansion might take place, but, it won't really tell you what the expansion was at what depth.

High speed cameras and ballistic gel are needed for that.

Both of the bullet penetration formulas that I mentioned above address all of those issues and both are quite valid for their purpose.

 

[James K]

NO. Unless you expect to be attacked by a block of ballistic gel, there is no way of predicting penetration for the simple reason that an animal (including human) body is not a homogeneous mass. Further, if the idea is to stop an attack with killing an unfortunate (for the attacker) but secondary result, a shot that breaks the hip bone may be more immediately effective than one in the chest.

Books have been written about the effect of bullets on the human body (the MacPherson book is a good one), but they describe what usually happens when a bullet hits a specific point, something not even a skilled shooter could guarantee under stress.

Jim

 

[saltydog452]

Nyclad at std pressure

Federal's Nyclad is dead soft lead construction.

Using the parameters that were set in Post #1, bullet construction wasn't a player in what should be considered..

I'd think construction should be the first consideration in prediction of downrange performance.

salty

 

[481]

NO. Unless you expect to be attacked by a block of ballistic gel, there is no way of predicting penetration for the simple reason that an animal (including human) body is not a homogeneous mass. Further, if the idea is to stop an attack with killing an unfortunate (for the attacker) but secondary result, a shot that breaks the hip bone may be more immediately effective than one in the chest.

Books have been written about the effect of bullets on the human body (the MacPherson book is a good one), but they describe what usually happens when a bullet hits a specific point, something not even a skilled shooter could guarantee under stress.

Jim

Do you have a link to source(s) that supports your refutation of either of these models?

Many folks mistake testing in ballistic gel as the equivalent of shooting into a human body when in fact it is not. Ballistic gel is a test medium that is scientifically correlated to swine muscle tissue, which in turn is comparable to human muscle tissue, that duplicates the average density of the human body -including bone. Ballistic gel is used instead of actual muscle tissue because it permits the careful control the properties of the gel, allowing for consistent and reliable comparison of terminal ballistic performance. This PDF explains quite well:

http://ammo.ar15.com/project/Fackler_Articles/effects_of_small_arms.pdf

Despite such misgivings, it is possible to reliably model the behavior of a bullet in ballistic gel.

 

[Derbel McDillet]

Unless you expect to be attacked by a block of ballistic gel, there is no way of predicting penetration for the simple reason that an animal (including human) body is not a homogeneous mass.

Gelatin represents "typical" soft tissues.

There is no practical difference between various soft tissue densities encountered by a penetrating bullet.

More than two decades worth of OIS data shows penetration performance in ordnance gelatin reasonably represents penetration performance in the human body. The ONLY major difference is when the bullet encounters bone.

 

[Pond James Pond]

Unless you expect to be attacked by a block of ballistic gel,

As it happens there have been two incidents of aggression reported recently and there are several shady blocks regularly hanging out on the corner of our street.

But don't worry: I know their game. I can see right through them....

 

[WESHOOT2]

"Hit 'em hard hit 'em fast hit 'em often"?

There is no reliable predictor mathematics for shooting people.

There is a large body of anecdotal evidence.

 

[2damnold4this]

It is the age old issue of round choice and I have two options that I have simply because they are available and others are not: both 158gr, both manage about 800fps/250ftlb at the muzzle (adjusted to snub performance), both have a flat nose.
One is FMJ, the other SP.

I have touched on this issue in the past and got various responses mostly pointing to the flattest, widest meplat possible and so far these two rounds are it, aside from WC although those are pretty weak loads with 670fps and 150ftlb at the muzzle (also adjusted to snub performance).

I want to know if the SPs would yield any worthwhile expansion and if, in doing so, would it still retain any decent penetration.

I don't think any of the rounds you mentioned are going to have problems penetrating soft tissue. If I couldn't use a hollow point that did well with the FBI's testing protocol, I'd use the full wadcutter.

 

[Pond James Pond]

I'd use the full wadcutter.

My only reservation is that WCs, looking at those I can get, have 60% of the muzzle energy and 70% of the velocity, when compared to the two jacketed variants. Not to mention having 9gr lighter bullets.

 

[Derbel McDillet]

My only reservation is that WCs, looking at those I can get, have 60% of the muzzle energy and 70% of the velocity...

Forget about muzzle energy. It's meaningless. The idea is to poke holes in vital soft tissues.

Both your flat nose FMJ and SP will produce less wound trauma than a wadcutter.

"Target wadcutters offer good penetration, cut tissue efficiently, and have relatively mild recoil. With wadcutters harder alloys and sharper leading edges are the way to go. Wadcutters perform exactly the same in both bare and 4 layer denim covered gel when fired from a 2" J-frame."

-- http://pistol-forum.com/showthread.php?4336-BUG-s-380-ACP-vs-38-Sp​

 

[Hal]

Both of the bullet penetration formulas that I mentioned above address all of those issues and both are quite valid for their purpose.

I don't see how or where.
Maybe I'm blind or stupid..

 

[481]

I don't see how or where.
Maybe I'm blind or stupid..

You? Blind? Stupid? I doubt it.

Have you read either book?

Both books (and models) address the effect of how a bullet's sectional density changes during penetration as well as the 'dynamic equivalence' of gelatin and H₂O and in a sentence, either of the two models replaces the need to rely on the old, but unproven, axiom:

"Divide penetration in H₂O by 2.00* to get the equivalent penetration in gelatin."

* or by 1.80, or 2.25, or 2.50, or 3.00, or any other unproven divisor that seems to fit the relationship

 

[Hal]

481 - I'll take your word for it.
As I get older and older, I've become more of a visual type.

I like the ease of seeing something in a video - such as the bullet going through the gel - and the way it's path & the shape of the bullet is right there to see.