Hi I have a M4 Type Carbine, with a m16 bolt carrier group in it. I want to by a Spare Back-up bolt carrier group new from a Colt Supplier. Can I switch bolts in the rifle with out re head spacing? The M4 Carbine I have has only 40 rounds Shot thriugh it. I just want to have a Back up Bolt that I can just drop in. Can this be done or is the head-spacing a problem any info will help. Thanks wedgemo:)
Buy your spare BCG. You should have no issues as long as you are using a quality BCG built to the Mil-Spec dimensions/tolerances. Head space is mostly only an issue with well worn barrels.