01 January 2013

Firearm Lethality: Moving away from lead

The current trend in projectiles is away from lead, or in some cases, using less lead.

In the previous post we took a look at Dr. Martin Fackler's effects of terminal velocity on a 5.56 caliber bullet.  Velocity causes bullets to break up on impact, and this is largely because lead lacks the tensile strength to hold together with that much force acting upon it.

Previously we covered how a hollow point pistol bullet works, using a hydraulic effect to open up the bullet.  When velocities are at the opposite end of the spectrum, the problem becomes keeping them together until they penetrate enough.

How much penetration is enough?  Depends on what you are shooting.

Bear Claw Bullets, from American Hunter
First, let us take a look at bullets that use "less lead" such as the Trophy Bonded Bear Claw.  This bullet uses a long gilding metal tail that will hold together at all known rifle velocities, no matter what happens to the soft lead nose.  The compromise with this design is that weight retention can go down if velocity strips enough of the lead away and leaves mostly copper gilding metal behind.  As long as you are shooting a bullet appropriate to the animal you are hunting, I wouldn't worry about under penetration even with some weight loss.
Evidently there were people who worried about weight loss though, and here is one of the answers.  First up is the Winchester Fail Safe.  Lead is used in this projectile as ballast, to make the projectile more massive (in the physics sense) and therefore have better penetration.  Note the expansion of the lead base into a "fan" shape after use, that hydraulic effect that caused pistol hollowpoints to open up is at work again here, but from the other end.  At the level of force acting on the bullet you can think of the lead as a "semi liquid" that is sloshing forward to put lateral pressure on the gilding metal jacket.  As you can see the thickest part of the gilding metal underneath the hollowpoint and ballistic tip did not expand much at all relative to the nose or base.
Winchester Fail Safe
Fail Safe After

 Other than solid gilding metal bullets like the Barnes X bullet this is pretty much "state of the art" when it comes to lethality for hunting big game.  For hunting varmits older bullet technologies are preferred because they are cheaper and deliver the results expected.

Shifting gears a bit, and shifting the intended target of the bullets, we'll go to war.  Specifically war against the Nazis.  The US Military maintained the use of the 30-06, and despite having a very good long range round in the M1 Ball loading, adopted the M2 loading because it had less recoil, and at the short ranges where the National Guard could train there was no ballistic difference between M1 and M2 ball loads.

Sectioned 30-06 AP.  Photograph by Carteach0
The Black Tip "Armor Piercing" 30-06 loads were built differently, and will be the first bullet in this series to include steel in the design.  The AP bullets were made by drawing the jacket, inserting a small amount of lead into the nose, inserting the steel penetrator, and rolling the heal of the bullet like a normal FMJ.

If you haven't read Carteach0's investigation into 30-06 Armor Piercing ammunition, now is a good time to do so.  http://carteach0.blogspot.com/2012/01/30-06-m2-armor-piercing-bullets.html 

A generation later by blood, or two generations by small arms development, the armor piercing properties of the 5.56x45 cartridge were noted, and a Belgian designed bullet, the SS109, was adopted as NATO standard to increase the penetration of service bullets against Soviet mild steel helmets.

What should be noted, is that the steel moved forward in the bullet compared to the 30-06.
Israeli, Bosnian, Lake City, unknown Photograph by Wolfganggross AR15.com
I can hear you asking, "AM, why is the placement of steel important?"  And the answer is, notice the air gap on three of the four bullets sectioned.  Remember what Carteach0 found about the accuracy of 30-06 AP?  When the lead shot deteriorated and left a gap, accuracy went to crap?  The accuracy standards for M855 ammunition were built around machine gun level accuracy, so a rifleman who wants to shoot tight groups should probably steer clear of most SS109 projectiles.  From personal experience, expect about 4 minutes of precision from a good rifle from field positions.

Now with the current war on terror, the underfed religious fanatics don't particularly have a whole lot of meat on their bones to stop a bullet hiding behind things like cars, windows, doors and such, and so the military went around trying to fix a marksmanship problem with a bullet solution.  The Navy and USMC came up with Mk 318 SOST. 

If you think the Mk318 SOST looks an awful lot like the Trophy Bonded Bear Claw, give yourself a pat on the back.  Reports from the field have been positive, although I would take that with a grain of salt for now.

Prototype left, final M855A1 right. Photo by Wolfganggross
The Army, in a show of common bureaucratic money wasting, went with another solution, an improvement of M855 by getting rid of the lead and making the steel part bigger, and out front.

There were a number of different tail configuration, bismuth/tin allow shown as a prototype.  I heard about a nylon heavy metal composite being tried as well.  In the end, the bullet that flew the best was the solid gilding metal base

Notice that the steel penetrator is fully out front. So you can see the evolution from "steel insert behind lead" to "steel insert in front of lead" to "steel insert without lead" over multiple generations of small arms testing.

So far we have looked at bullets that have been designed to stay together through thick hide and muscle, shoot through Soviet helmets, and finally through car doors and windshields. 

There have been other attempts to make "armor piercing" bullets.  Initially an extra thick jacket on a 53gr FMJ was used in 5.56x45.  Later a tungsten core was used in M993.  I mention these because you might find some around, but neither ever saw the widespread usage that 30-06 AP, M855, or M855A1 has in peace and war.


Nathaniel Fitch said...

Why do you think the forward-placed steel core of M855/SS109 affects accuracy negatively? I have found that the accuracy of the SS109 or M855 you are shooting depends greatly on the source. I have found that Lake City M855 produces the sort of 4" groups that you describe, but for instance PMC Green Tip-LAP (which I believe is M855 spec, not SS109) produces very normal 2" groups from my well-shot Colt 6920. This seems to weigh in against the theory that the forward-placed steel core of SS109/M855 necessarily reduces accuracy, and more supports the idea that it simply depends on the standards by which the ammunition was made (which is true of all ammunition). The current US military accuracy standard for M855, for example, is relaxed to about 5.5 MOA, due to the large volumes that are required of the single Lake City plant. This post by Molon on ARfcom also provides support for this.

AM said...

Nathanial Fitch,

The steel penetrator in M855 isn't always perfectly centerred, which increases the yawing motion of the nose as it is now slightly more off balance.

When you are competing and the 10 ring is only 2.2 minutes, you can see how using a 5.5 minute ammunition is not desireable to be competitive. Although it has been my experience that most lots of Lake City M855 will be fine at 200 yards as most lots shoot tighter than the acceptance minimum.

Still, as the distance increases and the velocity drops the more susceptible a bullet is to yaw and course deflection the larger you can expect groups to get. Things that don't matter so much at 200 yards matter a great deal more at 600 yards.