A tight chamber will theoretically give higher presure with less of a given powder charge...but doesn't sound like the problem as who cares the charge as long as you are a heaving the normal Bol range...
Premature presure signs are something I have addressed before....distance to throat can be a problem...causes a spike in presure ...usually seating depth can remedy this...but if I were you I would consider doing a chamber cast and see if the neck may be too tight....I had a reamer one time that cut too tight of chamber and nec..I don't recall the cal but I got it from a retired gunsmith and it appeared to have been re sharpened..I just replaced the reamer...the old ones are just used for roughing...
