I have attached a bullet velocity chart. This gives a good reference for velocities out of various barrel lengths. The key to the 5.56mm round doing any damage is its ability to fragment. Generally speaking it will not fragment at velocities below 2,700 fps when it hits something. So looking at this chart, you will lose velocity the farther it gets away from the barrel. In a CQB situation, generally you should not ever see anything more than 25 yards. You will also be better off with a 11.5" barrel , because the 10.5" will be borderline. 55 grain ammo would be better with a shorter barrel because it is slightly faster than 62 grain and will fragment better.
As for penetration of body armor, any of these figures would penetrate level IIIA at these ranges.
Last edited by blhar15; 10-02-09 at 07:41.
When the people fear their government, there is tyranny; when the government fears the people, there is liberty.
Glock Certified Armorer, AR-15/M16 Certified Armorer