Aloha Shooterx:
IIRC, the inner diameter of my SA MB was larger than a standard M14 FH. Bullets should not contact the sides exiting the barrel. If your barrel splines and MB are cut correctly (assuming they are), removing and installing the new one should be easy and straightforward. If the splines are a little on the tight side that is good and may require a wood block or dowel to tap it off or back on.
There is a set screw that holds the castle nut in place and must be removed first prior to removing the castle nut.
When reinstalling the new MB, use finger tight to screw the castle nut in place which will pull your MB into place. The castle nut pliers is then used to do the final nudge to get the castle nut's notch in place so the set screw can be replaced.
You should have a set of allen wrenches, the castle nut pliers, a wood block or dowel, small hammer available to do this job. It is a simple job. If you move your front sight to the MB as well, it should slide right on but may need to be "stoned" a little if it's too tight.
Good Luck... and take your time... :lol:
Aloha,
Tom O.