I have seen this before.
In some cases it's a piece of old primer that's gotten blown into the bolt body and it gets between the shoulder of the striker and the bolt itself.
Take a 45 cal cleaning brush and clean out the inside of your bolt body. Clean the forward shoulder of the striker too. If something is stuck on the striker, it's very visable, but if you didn't look for it, you might miss it.
I can't say that's whats happening to you, but it sure sounds like it:)
SZ