Originally Posted by 444
But with rifles, people endlessly discuss military ball ammo. We worry about the velocity that military ball ammo fragments, tumbles or whatever instead of just using soft points or whatever.
The problem with alternative bullets for use in an AR-15
in an anti-personnel role, is that the 5.56 bullet lacks the mass to impart most of it's energy on the target the "good, ol' fashioned way" so to speak. It's a tiny bullet. Without fragmentation, it'll just cruise on through the target. And even if it expands, it wont expand enough to create a lethal wound channel very reliably.
However with fragmentation, 5.56 FMJ wound cavities over a
foot in diameter have been witnessed--far in excess of anything even the venerable .30 cal can do, and superior to the 7.62x39 our soldiers typically face today. In fact, during the initial field testing of the M16 in Vietnam, veteran combat soldiers (read: WW2 and Korean War guys, MACV-SOG types) were reporting that the early 1:18, 1:14 and 1:12 twist M16s were literally blasting and tearing chunks of flesh off the Vietnamese and Chinese enemy. Many were reporting that the wounds caused by the then-new M16 were the most disgusting they'd ever seen.
Now, not every report from soldiers can be relied upon because they often lack quintessential knowledge to understand what they're seeing, but this is one case where the field reports were fairly consistent. There's even pictures to support the anecdotal evidence, and Martin Fackler's research supports it as well. The reason for the supposed "ice picking" that so many soldiers seem to complain about today is due, in part, to either a misunderstanding of terminal ballistics (ie: everyone is different and will react differently to being shot) or Ordnance's "cult of accuracy" winning over common sense and field experience, and demanding more accurate rifles and tighter twist barrels.
The tighter twist of these barrels creates what some call "over stabilization" (technically there's no such thing). What's really happening is that the tighter twists reduce precession. Precession is that "wobble" that bullets do as they fly through the air. Every bullet wobbles at little, but the degree at which it does it is affected intimately by the barrel's twist. Now, common sense tells you that if you want more accuracy, you reduce precession and keep the bullet stable longer, and to do this, you usually tighten the barrel twist up.
However the problem is, is that precession is actually a
good thing for terminal ballistics with respect to Spitzer type bullets. As we know, fragmentation of the 5.56 bullet is accomplished by violent yaw at impact. The centrifugal forces the bullet undergoes when it begins to spin end over end overcomes the structural integrity of the bullet, and it comes apart. To the crux: the faster the bullet yaws, the more violent and "explosive" the fragmentation. This is the velocity component, and precisely why the 5.56 needs to be going a certain speed for fragmentation. Below that threshold, the physical forces on the bullet in yaw wont be high enough to cause explosion inside the target. But also and just as importantly, the more the bullet wobbles through the air, the sooner and more violently the bullet yaws. This is the precession component, as the bullet will hit the target at a greater angle than it would from higher stabilization.
Long story short: somewhat less stabilization is beneficial to Spitzer bullets, especially with a long ogive and accentuated rearward centers of gravity (this exacerbates the bullet's desire to reverse itself and yaw hard). Eugene Stoner understood this, which is why he designed the AR-15 with a looser twist, and designed the rifle to be a 3-4 MOA gun (looser twists are less accurate with the 55-77 grain bullet weights). Stoner understood that modern engagements would be close up, so the focus was on a lightweight, high capacity bullet hose that would blast the enemy to bloody pieces.
But unfortunately for Stoner and generations of future soldiers fielding the M16 and M4, America is a nation of riflemen and there was pressure to accurize the rifle immediately at the start. Over the years, the mil spec has called for increasingly tighter twist rates...And the bullet weights given to line troops have not changed at all, thereby reducing the 5.56's combat effectiveness.
Fragmentation is
key for lethality in the 5.56 round. It's too fast and lacks the mass to dump energy through expansion and the traditional methods we rely on with larger, heavier bullets. So the problem isn't FMJ bullets, but rather a relationship between velocity and twist rate. Tweak those and you'll see a return of those disgusting and highly lethal wounds that SOG guys were seeing in Vietnam in the early 1960s, and the whole argument about finding alternative rounds to the 5.56 FMJ will cease to be relevant.