Bolt swapping

[Cincinnatus]

I noticed when perusing the Army/Marine Corps Operator's Manual for the M16, that it says not to swap bolts or BCGs between rifles. I assume this is for worn BCGs and Bolts not new or unworn BCGs and bolts because a worn one put in a different rifle might affect headspace with the barrel extension, correct? Or is there some other reason for this such as simply keeping parts organic to a given rifle without mixing them up--in other words, a logistical or orderly concern rather than a technical one? I wondered about this because I always thought it was fine and well to drop in any BCG or bolt into any AR without any problem.

[6933]

Swapping them could cause a headspace issue. Buy a G.I. gauge. Got mine from Bill Ricca after Gunz told me about them. Might not have have them anymore. Worth checking.

[4thPointOfContact]

If I recall correctly, part of the Mil-Spec procedures is to completely strip down 10 rifles to component parts, mix up all the parts and then assemble 10 rifles that must meet all tolerance specifications.

I've also heard that bolts will 'wear in' to the lugs on their respective rifles. I tend to believe both parts, so I won't be exchanging bolts that aren't new and unused.

[Iraqgunz]

Obviously the purpose behind it is to prevent an accident. Since the average joe has no idea how many rounds have been though his weapon when he is issued it is easy to understand how swapping parts could lead to a headspace issue. The same warnings are also in the M249/ M240 manuals.

The bolt carrier plays no role in the equation at all. It is simply the bolt and barrel extension.