Normally with other type of rifles. I would disassemble the bolt and try some of my resized brass just to make sure as I use a drop gage to test sizing while working. My PTR (I also have a 91 same phenomena) bolt gap is at a steady .457mm. I thought well I'll just drop in a piece of brand new IMI brass (it was at the min length of the drop gage) I drop the bolt pull the trigger and look at the gap. Lo and behold the gap jumped to .610mm. I then tried a piece of sized brass that was at max length in the drop gage. It came in at .639. I don't get why the gap is growing as the brass length increases. Any ideas?