I was shooting a British FAL rifle at the range today, and was using .308 Win commercial ammunition. We were assured by the gunstore that there was no difference between .308 and 7.62x51. I have done some surfing, and found that this is not necessarily true. The .308 is hotter. Today we were finding that the .308's, in spite of having a higher pressure, were not cycling the rifle. the gas system was open,(not on the grenade setting), and the gas regulator was set on "0", the bleed off shut tight. At these settings, there should have been no bleed off of gas on firing, with all the gas going to cycle the rifle. But the rifle only short stroked, I saw the chamber open about 1/2 way with no extraction of the fired round. There were no signs of excessive pressure in the fired cases, except very flattened primers. What is going on here? The inch pattern FAL was put together by DSA using a new receiver and barrel. I probed the gas bleed off hole between the barrel and the gas cylinder, and it is open. Bought some Lake City NATO 7.62x51 rounds, and will try these tomorrow. These have a rated pressure that is lower than commercial levels, so I don't know why they would work better. What am I doing wrong?