I'd been wondering this for awhile. I want to get the Miad Core Insert that carries the Xtra BCG and thought I'd see what tweaking needs to be done.
If you have a spare BCG for your M4 does it need to be fitted, headspaced or what? Is it like having a spare fitted 1911 extractor or just plug-n-play?
Should it be or would it be best to have an "exact" duplicate?

