The only chambers I've reamed in situ have been in barrels that were short chambered, specifically Criterion barrels for Springfields, that only required a couple thousandths of steel to be removed. A couple twists of the reamer for the extractor-less bolt to close on a Go-gauge. Oh, and a couple .30 barrels that I altered the throats with a 1 1/2degree included angle throating reamer (for specific cast bullet fits). All turned out great because they were securely piloted and intrusion was so minimal that the cutting oil was barely discolored by steel chips.
I wouldn't think of conducting any more reaming than what I described with the barrel in the receiver. Barrel removal is too easy, but I witness a lot of guys who have an almost pathological fear of removing a barrel - it's almost like it's considered Black Magic or something.
