5.56 mm

[dj1leg]

For all the experts out there...

If you have read the Blackhawk Down book, I have a question. The Delta guy that was primarily interviewed, (I think his name was Howe), complained about his 5.56 ammo where he shot a number of somalis four or five times and they got up and ran off clutching their chests. Now if this is how it is for the armys green tip round where it goes right through them unless they hit the brain, heart, or spine, why don't they switch back to the old 7.62 round where one shot knocks you down? See what I'm getting at? A friend of mine told me that the 5.56 ammo was designed to "jump around" inside the body.

[Mac679]

somewhere I seem to remember JY mentioning part of the problem being that the rate of twist in more recent variants of the M16 are overstabilizing the bullets so they don't tumble around on impact as much any more if at all. Another thing is that the new green tip ammo ( M855 ) is 62 grains and contains a steel core to help defeat body armor. The old ammo was 55 grains and had a lead core. Combine all those factors and that the Somalis weren't wearing body armor and you can see how some of the problems came about. I'm not up too much on all the details and if I missed anything I'm sure someone else here can fill in the gaps.
Mac

[recce_o]

Mac, you are correct, the M16A2 round is over stabilized. In addition to the temporary wound cavity that results from high velocity ammo, the 5.56mm round has an additional wounding mechanism. With the old 55 grn ammo the bullet would begin to yaw in soft tissue, this would put stress on the bullet causing it to fracture at the cannelure. This resulted in segmentation of the projectile into two pieces, with some ancilliary fragments. As you may imagine, the wounding cause but such a round was fearsome.

The M16A2 has rifling of 1 turn in 7". The M16 and M16A1 had rifling of 1 turn in 12". Generally, the reason why they had to switch to the faster rate of twist was because of the switch to the longer 62 grain bullet. However, the ultimate reason why they chose 1 in 7 was to stabilize the even longer tracer ammunition. In fact, 1 turn in 9" is adequate to stabilze the 62 grain bullet. With the one turn in 7 rifling there is less fragmentation and greater probabiliy that the round will exit the target without having tumbled or fragmented.