I've successfully worked on a number of A bolts..... Most recently did a 6.5 creedmoor for my daughter on an old browning. Micro medallion action and a bartlein featherweight tube and McMillan edge technology stock...... Awesome little rig, just over 8# with a scope and a dream to carry.
some of the barrels can be tough to break free from the actions, stainless especially..... Nothing different as far a headspace goes from other actions but the tennons have very fine thread pitch, 1"x20tpi on my older ones to 1x32tpi on my newer ones.
no reason to worry about an A bolt but I'd suspect a BAR is a different story, no experience with them at all.