Originally posted by: Mookow
Again, Type III body armor will stop a 5.56 NATO FMJ fired from an M-16. Which means you are SOL unless they are wearing III-A or lower. And even then, most tests of body armor using the 5.56mm are using an M-16 length barrel firing a FMJ round, not an M4 firing a hollowpoint. An M4 gives you a significantly lower velocity (due to the shorter barrel) which translates into less penetration. Will a 5.56mm JHP round out of an M4 penetrate Level III-A armor? Probably, but maybe not. I wouldnt want to be the test dummy for a test of that. OTOH, I wouldnt like to stake my life on it penetrating with enough velocity left over to stop the target. However, in general, I'd rather be packing a SMG chambered in 40 S&W, 10mm, or 45 ACP, because most of the time they will NOT be wearing armor, and the pistol cartridges I listed (especially in +P) will incapacitate a target faster than an M4.
The reality is that any cartridge is a trade off. It'd be nice to carry a gun that would reliably penetrate a Level IV vest, and put the target on his @ss first time, every time. But anything that fires the 50 BMG is a little heavy to walk around with all the time

. So you have to make trade offs. It is just my opinion, but the 5.56 NATO is not a good choice when your primary application is shooting people. "Shooting people" isnt the PC way to say it, but
cops do not carry guns to shoot rats with, they carry them because on infrequent occasions they need to shoot someone. If I want to shoot someone, I'm not looking to wound them, I want them incapacitated as quickly as possible, and often that translates into "dead as quickly as possible" in a real world scenario. If you are going to shoot at something, you had better make sure you are OK with the repercussions of killing it, because guns are designed to kill, not wound (rubber bullets not included, but OTOH the guns in discussion were not designed around rubber bullets). On a military logistical scale the "wounding, not killing" aspect of the 5.56mm might make sense. When you are the guy pulling the trigger however... well, no one likes to have to shoot someone 5 times to get them to stay down. Which is something many of our troops have had to do, especially when engaging a target at range with an M4.