Colt M4 C stamp & keyhole 16” question

[clark33]

I have a colt m4 16” upper, it has the C stamp and keyhole.
Barrel is also stamped C MP
Curious what this means, are they more desired? I bought it new a few years ago and it hasn’t seen much action in the last few years.

 

[1911hombre]

Keyhole is forge marking. C MP on barrel means "Chrome-Lined, Magnetic Partical inspected."

 

[rpoL98]

keyhole is the forge marking for Cerro Forge, common. Other popular forge markings used by Colt are the square for Brass Aluminum Forge, and Anchor Harvey. Also Alcoa. and there might be a few other stragglers. not sure about Mueller or Cardinal, others would know.