01 January 2013

Firearm Lethality: Non Lead Solids

When you are trying to get the most penetration possible experts turn to the toughest bullets on the planet, monolithic solids.  We covered armor piercing/barrier blind rifle ammunition for military use in the previous post, but the key take away here is that anything designed for deep, straight, penetration will also do well against barriers.

Bear Claw Left: A Square Solid Right: Photo Stuart Anderson Wheeler
These monolithic bullets are designed to hold together inside the toughest animals on earth at velocities much higher than the sedate 2,400 fps noted before in this series, although many of them find themselves being used in older rounds such as the 458 Win Mag which is generally kept around the 2,000 fps mark.  Solid gilding metal bullets like the Barnes X bullets are designed to expand in tissue at high velocity.  Bullets like the A Square Monolithic Solid are designed to penetrate deep and straight.
Barnes Triple Shock X Bullet, monolithic gilding metal

Some common sense comes into play here, you don't need a 500 grain monolithic solid to stop a charging Elk, nor would you use a 165gr expanding solid on Cape Buffalo.  At least not if you had any sense of self preservation.

Take note of the driving bands on the A Square and X bullet.  Traditional cup and core bullets do not need these as the lead core deforms easily, and the gilding metal jacket is thin enough that it deforms easily to take the shape of the rifling.  Without those relief cuts or "driving bands" the bullet would cause a very unsafe spike in pressures and give extremely bad copper fouling in the bore.

Remember, penetration is more important than tissue disruption when it comes to lethality, so expansion becomes the least important feature when selecting a rifle bullet.  However, if you are using a cartridge that is accurate, and fully capable of penetrating to the vitals, then choose an expanding bullet to maximize the lethality trio.

In the handgun world, monolithic solids have been labeled "cop killers."  Back in the 60's three men Paul Kopsch (coroner), Daniel Turcos (police sergeant), and Donald Ward (special investigator) started experimenting with solid brass projectiles so that Police could shoot "barrier blind" ammunition (same problem the USMC and Army had with M855 and why the USMC adopted Mk318 SOST and the Army M855A1).  They eventually settled on a solid brass bullet lubricated by polytetraflourinated ethylene (PTFE) or "Teflon."   If someone tells me that KTW stands for "Kevlar Tipped Wadcutter" ever again I may suffer a stroke.

For some reason Hollywood took note of the teflon coating and decided that any bullet coated with teflon was an "armor piercing cop killer" to the point where a normal FMJ bullet sprayed with "teflon" pierces a vest in the movie "Ronin" and Mel Gibson can shoot 9mm bullets through the blade of a bulldozer in one of the "Lethal Weapon" fiascos.  Teflon does very little for terminal ballistics, it does a lot to protect the bore of the pistol.  Remember how lead was very maleable?  Solid brass isn't.  Normal cup and core bullets deform easily against the rifling of a steel barrel, solid brass not so much.

KTW Bullets, truncated cone, PTFE coated brass
Anyways, you can thank the same mass hysteria that gave us "plastic guns" for the enduring myth of teflon bullets.  There are a lot of confusing laws on the books now that ban the "importation of armor piercing handgun bullets."  You are perfectly free to make them yourself on a mini lathe, but check your local laws.

Now, what is the future of monolithic bullets?  I don't know, but the most interesting idea has come out of Italy.  Compensated bullets.

With a "compensated barrel" a series of holes are drilled perpendicular to the bore which allows gas to escape sideways before the bullet exits the muzzle.  This is to reduce muzzle flip and recoil.  By drilling a hole in the base of the bullet and other holes perpendicular, the bullet acts as a compensator for a brief amount of time.  That the bullets are solid brass instead of lead means they are lighter (less massive) and can therefore be driven at a higher velocities.  Going back to our initial set of useful equations, E = .5MxVV or one half mass times velocity squared.

I can see the advantage of using this sort of bullet at relatively close range while retained velocity is high.  More controllable rapid fire, and barrier piercing capabilities.  I haven't had the chance to play with any of these, but I would like to.

The increase in velocity is key, reducing a 9mm mass from 125 grains to 100 grains will give you an increase in energy if you can add 40% to speed.  And since the projectile is brass, it can hold together on impact even with the added force acting on it.

However, the reduced mass gives a reduction in momentum as velocity decreases, so don't expect compensated bullets to be miracles of ballistics. 

I expect Hollywood to lead the charge in declaring these bullets (designed by a competitor for competitors) evil incarnate to make the importation even more illegal.

Other materials have been used for solids, such as Tungsten.  Tungsten is a good choice because it is denser than brass (ironically it has the density of gold) and is quite hard.  It makes such a good penetrator that several nations have stopped using Depleted Uranium (DU) fin stabilized discarding sabot rounds for the 120mm NATO standard main gun on tanks.  Tungsten is damn expensive compared to brass though, and ironically the animals don't seem to get any deader for being shot with it.

In terms of defeating ballistic vests, you either need a bullet that will punch through, or enough energy that the bullet design doesn't matter at all.  When gun banners talk about banning "armor piercing ammunition" they are really trying to ban all centerfire rifle ammunition, even in Grandpa's 30-30.  You can look up the National Institute of Justice body armor standards, NIJ 0101.04 for yourself.


Anonymous said...

Thank you for your thorough and excellent work.


D Anderson said...

I don't understand what the holes in the compensated bullet are suppose to do. They can't do the job of an actual compensator. Compensators work by direct gas upward and backward, which pushes the muzzle down and forward. The holes on the bullet are necessarily symmetric so they can't push the muzzle down, and directing gas backward with the bullet would only push the bullet forward, not the barrel. I suppose it might be able to accelerate the bullet a little bit, but the holes don't appear to point backward enough to do that. I wonder if they really do anything at all or are just a gimmick.

If you just want a lighter bullet, you could just hollow it out without putting holes in the sides, or use a lighter material, such as aluminum.

AM said...

D Anderson,

When the bullet is partially out of the muzzle, the bullet exposes those holes to the ambient atmosphere while a portion of the shank is still being gripped by the barrel. This allows some of the pressurized gas in the bore to bleed off before the bullet has completely left the barrel.

The pressurized gas will be leaving perpendicular to the bore, so all the gas that is bled off this way will not contribute to in line recoil.

A normal bullet leaves the bore like a champagne cork "popping" out of the bottle. The compensated bullet is more like a soda bottle cap that you have to unscrew really quickly and the overpressure soda still comes out before you get the cap off.

D Anderson said...

Thanks, that makes sense. I still wonder though if it makes enough difference to notice.

Thanks again for the quick response.

Roscoe said...

Thanks for mentioning the KTW slugs. I always thought they were tungsten under the teflon. Double checking it looks like only the early ones were tungsten. Thanks for the correction.

AM said...

KTW loads ranged through tungsten, steel, and brass. By the end, brass was the preferred material. Not as dense as tungsten, not as cheap as steel, but the best bang for the buck as far as cost to performance was concerned.

After all, once you have reached a desired level of penetration performance, anything beyond that is unnecessary.