Originally Posted by rocshaman
I was always told that my Colt SP1 would shoot 5.56 but I've never trusted that and always shoot .223 through the rifle. It has .223 Rem stamped on the side of it and that's what I use.
the sp1 is 223 not 556.
Originally Posted by FullautoUSA
What's really the difference between .223 and 5.56?
the difference is that the 223 has a shorter lead area in the throat than the 556. so when you load up a military 556 round its possible for the bullet to hit the lands and that creates an overpressure situation which can lead to a kaboom. this overlong situation is normally found in tracer and some ap rounds including the ss109 bullet.
if you are loading for a 223 using 223 data but are using military pulls you will still run into trouble. to know whether a given 556 is safe in your 223 you need to know the overall length from the bullet ogive and the overall lead EXACTLY in your individual rifle barrel then load under that length. this can also cause overpressure due to shorter length.
its dangerous to use military bullets in a 223 no matter how its stacked up.
anywayyyyyyyy its best to just stay away from military surplus and 556 in a 223 unless you really know the ins and outs of what ive glossed over above.