Quote Originally Posted by scottcc View Post
Could it be from AR Comp temp sensitive? As I stated it was in June and on a hot day at that. The ammo was in the trunk of the car. I was using metal 20 round mags, they were warm, then setting in the sun made them heat up more, while I was setting things up.

For what it's worth I do trim cases, check OAL and also shake to hear powder.

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Depends on just how hot your ammo actually got. There is a thread on another forum where a guy did some pretty elaborate temp sensitivity testing and found AR Comp pretty good, actually half the variation of Varget. But he only tested up to 165F degrees. Summer...Trunk of car...Metal mags sitting in sun while setting up. That metal mag could've acted like a miniature oven. Elevated ammo temp will increase pressure, maybe not to a degree that hurts anything in a "normal" range of temps but there's a point which it will change and it can change in a rapid and extraordinary fashion. Hard to know if you went past the line.

I suspect you had several things happen. 5.56 case, hot ammo, and a bit of bullet setback...OR...you just simply had a case head failure.