Terminal ballistics - balancing penetration vs. expansion (can we cheat?)

[the naked prophet]

I've been thinking about terminal ballistics and hollowpoints. For marginal calibers especially, there is a balance between expansion and penetration - too much expansion and it doesn't penetrate far enough to reliably hit a vital organ; too little expansion and even though it penetrates far enough it's less likely to nick that blood vessel or crush enough tissue to cause a disabling wound in the necessary time frame (ie. before you get shot).

So the quandary is that you need to increase wounding area, without slowing down the bullet so much that it won't penetrate deep enough.

As the bullet expands, it's frontal area increases, and with that also the chances of nicking a blood vessel or a vital organ as well as the drag on the bullet. But can you increase the "wounding effective" cross sectional area of the bullet without increasing the "aerodynamic effective" cross sectional area?

The idea was inspired by pictures of a 158 grain LSWCHP that had expanded in water (I saw it at www.hipowersandhandguns.com - I believe Mr. Camp is a moderator here). It was smooth, with a circular parachute or mushroom shape. Compare that to the shape of a Golden Saber or Gold Dot that has expanded but is more petal-shaped, with space between the petals.

What these bullet makers have done is increased the wounding diameter of the bullet, while reducing the drag on the expanded bullet. I don't know if this was their intent (consciously or unconsciously), or if that was only a byproduct of the "expansion through clothing" problem.

If you take that to its logical conclusion, what would be the best bullet design? Something that would expand rapidly upon impact, with a very wide spread of sharp aerodynamic petals (the reduced drag would allow it to penetrate deep enough while the very wide spread ensures the widest possible wound track)?

I have an idea in mind, but I'd like to hear other opinions first.

 

[Soybomb]

I think the problem is the marginal calibers don't offer all that much penetration even without expanding. For instance lets look at some .32 rounds from a keltec http://www.goldenloki.com/ammo/gel/32acp/gel32acp.htm . With no expansion you're getting 13-15" of penetration. When you do get expansion of 30% that falls down to 8-10" of penetration. With the bigger calibers we can usually do closer to 100% expansion. I think the amount of expansion you could get while maintaining a reasonable amount of penetration wouldn't be enough to bother with.

 

[RyanM]

IIRC, according to MacPherson, petals don't really make a huge difference.

Width of the projectile doesn't make that huge of a difference with probability of hitting something vital. If you hit 1" away from the heart, that's complete miss unless you've got a 2.0 caliber gun, and it would take a 3 or 4 caliber to do any meaningful damage to the heart. On the other hand, petals do make a slightly bigger effective hole.

But bullets that expand with petals have several drawbacks. The petals tend to be much more fragile, so if they hit something like connective tissue, they'll get folded back and have a reduced diameter. That can also happen if the bullet is driven at too high a velocity. Like if you look at the Steve's Pages terminal ballistics (http://www.stevespages.com/page8f.htm) many of the bullets that expand that way have the petals folded back against the bullet shank, and that's just from coming into contact with plastic from milk jugs. All-copper bullets and Remington Golden Sabers have stiffer petals, so they're more resistant to that, though.

Also, when driven at too low a velocity, or partially clogged with hide or clothing, petal bullets will often fully expand on one side, and remain completely unexpanded on the other, which isn't very good performance. Under similar conditions, most of the standard hollowpoints will make a partial mushroom, with less tendency to be extremely asymmetrical.

They can also be more fragile against hard barriers in some cases. For instance, the Barnes X-bullets and Triple Shocks in rifle calibers are horrible glass penetrators. They tend to lose all their petals on impact with the glass, leaving a very small diameter bullet, around .35" to .37" or so for a .30 caliber. The best glass penetrators are the plastic-tipped rounds.

Something similar could apply to a bullet which strikes bone early in its penetration, before it's expanded, like if it hits the wrist. A petaled bullet with thinner, weaker hollowpoint walls may get completely collapsed, or shed its petals so it can't expand, while a thicker standard hollowpoint might still be able to expand somewhat. A plastic-filled hollowpoint would probably also excel here, but unfortunately the only commercially available handgun ammo in service calibers I'm aware of is Cor-Bon Pow'R'Ball ammunition, which tends to exhibit low penetration.

So in general, petal designs are less robust; there's more that can go wrong with them. And at the very low power levels of tiny calibers, that's the opposite of what you want.

Although I'd say that Remington Golden Sabers and Winchester Ranger Talons are an excellent balance between petal and normal. The lead core expands fairly normally, while the jacket forms the sharp-edged petals. Dr. Fackler has spoken very highly of bullets like Black Talons, Golden Sabers, sharp-edged full wadcutters, and other bullets which add a cutting element to their wounding effect. They tend to do better than other designs, for a given penetration and expanded diameter.

Probably the absolute most efficient bullet would be something with very very low cross sectional area. Something like either a broadhead arrow, or an airfoil (a tubular bullet that's completely hollow inside).

 

[fineredmist]

Big slow moving flat nosed hard cast lead bullets are the answer. They break bones with little problem, produce wound chanels similiar to HPs and they break out on the far side. A semi wad cutter in .45 cal would be devastating in normal handgun range.
They still go on after the HP has lost it's punch.

 

[conwic]

Thank you , RyanM, for your very illuminating comparison of petal and convential JHP's. I had been wondering about that for a long time.

Thanks again- conwic

 

[the naked prophet]

Ryan, that was a very thoughtful and knowledgeable analysis. Exactly what I was looking for!

The design I had in mind though would use steel petals, precisely because the petals are weaker. I'm thinking of a number of knife-shaped steel petals making up the hollowpoint, with a lead core for weight. When it expands, it would be more like that broadhead arrow you mentioned, but with maybe six petals.

I took a class on "compliant mechanisms" a few years ago, which is the idea that flexible materials (plastics, springy metals, and normal metals at high stress loads and low cycles) can make simpler, more efficient machines. I'm thinking that you could make the steel knife petals expand very easily and dramatically, with over 1 inch diameter yet as little aerodynamic drag (and therefore as much penetration) as the deeper penetrating hollowpoints.

As a side note, interestingly enough, I had read that the DPX bullets (the solid copper ones, right?) penetrated barriers (especially glass) much better, due to the solid construction and the lack of a jacket to peel off.

 

[RyanM]

Interesting idea, but the main problems I see are legality and ease of manufacture. Anytime you put any kind of steel in the bullet, you're asking for the BATFE to say you've got an armor-piercing design.

An alternate design may be to use a brass-jacketed hollowpoint of relatively standard construction, with a jacket that gets thicker towards the base. During the manufacturing process where the jacket front is formed to the bullet tip, rather than just smashing it against the bullet and then scoring it, as is typical, the machine used would apply something like the star crimp that's used on blanks, but with the inside edges folded very tightly, so there are no peaks and valleys on the outside, just 5 to 8 (depending on caliber) very sharp, small peaks on the inside. Then the jacket would be scored between the peaks.

Properly engineered, such a bullet would expand similarly to a Golden Saber or Ranger Talon, with the sharp peaks on the jacket exposed to cut flesh. At handgun velocities, they'd probably cut fairly well, despite the relatively dull edges.

Alternately, the jacket could be lightly scored and then "crimped" over the core, so that it splits at the peaks. Then instead of one "blade" per petal, you have two.

 

[the naked prophet]

I was thinking that, like the 62 grain SS109 (or is it the SS190?) loading in the 5.56mm that is mommy-approved for our use, the actual core is lead, with only enough of the hardened metal for the opening petals.