I thought I was having a similar problem and mine was falling out of battery. As it turns out, having only had the gun a couple weeks, I wasn't quite putting it in battery to begin with. Between the pressure from rotating the bolt and that extra half inch of stroke for the 3.5" chamber beyond what I was used to I just wasn't quite putting enough umpfh behind it. I'm sure this is not your problem from the sounds of it, sounds like you definitely would have noticed, but anyone else that spits out the occasional live shell may want to slow down and check what they're doing.
