I bought some Winchester 55 grain FMJ .556 ammo recently and noticed this label which I have never seen before:

"This 5.56mm NATO ammunition is loaded to the same specifications currently used by our U.S. Military. The higher pressure in these rounds deliver increased velocity and energy over standard 5.56mm ammunition, which also promotes reliable cycling in modern 5.56mm semi-auto rifles."

"Notice: Use only in modern 5.56mm firearms in good condition. These Cartridges are loaded to military velocity and pressure which is higher than standard 5.56mm cartridges. The average pressure is 10% higher than the industry standard pressure for 5.56mm rounds."

http://www.cabelas.com/cabelas/en/templa...&hasJS=true

Seems like if you replaced 5.56 with .223 in certain places that paragraph would make a lot more sense...

5.56 is loaded to a higher pressure than 223. they are NOT th same.

+1... 5.56 expands more due to the higher pressure. Shooting 5.56 in a .223 chamber will cause probems unless it's designed for it example: Bushmaster Predator..This chamber's have extra head spacing to allow the expansion to accure with no issues. During my experience I have not seen a case get stuck in the chamber but seem primes pop out. WOW, kinda strange feeling primes hitting me in the head as I was shooting... Also primes were getting stuck in the chamber and causing FTF..

Hope my experiences helps the next follow THF member out. Thanks...