stock tube diameter

[urban spec-ops]

hi all

can anyone on here solve this really annoying issue i have. im trying to replace the stock on a mgc plug fire m4 for my friend. it currently has the old style ar stock but he wants the later standard look m4 stock on it. now for the issue airsoft stocks are too small and wont fit the the tube and im trying to determine for sure what size tube they were cloned from in real steel.

am i correct in saying the were roughly based on a commercial spec stock tube which if im right again has an external diameter that is slightly smaller than mill spec? if that is correct would anyone know if a mil spec stock would fit the plug fire tube even if there is a slight wobble

any help would be greatly appreciated

cheers

urban