Utah Rob,
Agreed there can be a problem there, that's one of the reasons we enlarge the flame channel when we do the conversion [it then absorbs more of the pressure] when we do the conversion. The other thing I have found is that primer pockets and how tight the breach closes affects that. I look for the right fit by trying different primers and one fellow in the club had a problem that did not fix and I had to put a thin shin under the block that holds the firing pin to push it out more to ward the primer so it would hold it well enough to seal. Lee