Help identify barrel w/stamp on underside?

[mechanicus]

Local dealer got old take-off upper in trade. 20" A1 profile w/.625 front sight. It has "C MPC" stamped on the underside of the barrel instead of on top. Obviously a Colt barrel, but could this indicate someone flipped and re-pinned it, or was this stamped this way @ Colt back when? Any input greatly appreciated. Mechanicus

[FMJ52]

It is normal for the C MP C marking to be found on the underside of the barrel. I have a number of them marked in this way.

[scottryan]

Normal.

I have an upper from a 604 made in 1970 that is this way.

[SpartanDCI]

I have seen Colt factory original 20" 1 in 12 rifle barrels, 11.5" Commando barrels and 14.5" carbine barrels with those markings on them under the barrel, just in front of the front sight tower. All were in the old Colt engineering offices in Hartford in the 1980's on the desk of the Colt M16A2 engineering manager, who was showing me a barrel comparison fro my work inquiry.....I worked for the Navy at the time.

If I remember right, the barrel code showed they had chrome chambers.