View Single Post Old September 30, 2012, 03:23 AM   #2 Metal god
Senior Member Join Date: April 10, 2012 Location: San Diego CA
Posts: 1,587 I do not know for sure but I think it has more to
do with the chamber of the rifle then the bullet it self . There
still has to be something else though .  Just copied this from
another site .I found it on the internet so it must be true
There is some overlap in the rounds, Im not sure of excact
numbers but basically the 5.56 maximum overall length is longer
then the max overall length for .223. So if you have a rifle
chambered on the short side of .223 specs some 5.56 ammo wont
work or be way over pressured when fired in the shorter chamber.
If you are buying an Autoloader for volume shooting you should
get a 5.56 chamber so you wont have problems with military
surplus ammo  There are some 223 Remington rifles in which you
wouldn't want to shoot 5.56x45 cartridges, some in which you
wouldn't think twice, and some that you'd want to check before
trying. CIP standards (E