It's been a long time since I've done any of this type work but it seems the firing pin block is unaffected because it is short enough not to come into play until the last 1/2" of firing pin travel. I don't recall gas vents on the bottom of the bolt although I once drilled some just because I thought it a good idea. As I said, it's been a long, long time. I'm hoping to learn from this post and am more than glad to admit my memory deceives me from time to time.