posted on Dec, 28 2012 @ 04:34 PM
Lot of confusion and BS in here, though a few people get it right.
Bullets are spun so that they are gyroscopically stabilized in flight. This reduces drag and keeps it radially symmetrical across the front of the
bullet. Exactly like throwing a football.
When a bullet encounters a resistant medium without having been stabilized, or if (typically the case) it loses its stabilizing spin, then it will
behave like any other object encountering resistance, and it will pitch over (tumble) so that the heavy end faces the direction of travel. What's
actually happening there is that drag is affecting the entire bullet but the heavier end has more inertia or something to power through it. Exactly
like dropping a half-full shampoo bottle off a roof; the full end will always land first, having pitched over in flight.
All boattail (rear heavier than the front) bullets tumble to reverse themselves when they lose spin and encounter heavy resistance (specifically,
Some .223 and 5.56 rounds are unusual in that they are very lightweight and weakly constucted, and move extremely fast for their size. As a result,
when they enter tissue and begin to pitch over, the bullet cannot handle the stresses involved and falls apart, with the parts going several different
directions still at high speed.
That's what causes large wound cavities from M193 where a .308 would put a much thinner line through the target (though again with a wider tunnel in
the middle where the bullet is temporarily sideways).
M855, as discussed, does not necessarily share this fragmenting characteristic, and is thus a poor choice for unarmored targets.
There's a new bullet being fielded with two-part construction designed to have both the weakness/fragmentation of M193 with the penetration of M855,
but I haven't heard much about it yet.
edit on 28-12-2012 by JBlitzen because: (no reason given)