When I went to Iraq, I brought a several Sig Sauer AR mags and the rest were regular GI issue. For my M9 I brought one personal mag and rest were GI issue.
I tested fired all them on the range and never had an issue with any of the GI mags. But I always figured as a Platoon Leader at the time, if I'm pulling triggers instead of managing the fight, it's gotten pretty bad.
"Our contract called for 16 cases of rifles and ammunition for $10,000 dollars, not a machine gun...........That is our present to the General"-Pike Bishop