Im just got a new M4 mutt It came with P marked internals, with exception to the bolt which has MP stamped on it.
Does anyone know what brand they are?
The “P” marking stands for Elisco. It can be found on the hammer, bolt, bolt carrier, barrel and upper receiver of Elisco M16s, 
Ya, I found that out about a month back. Have you seen the ones taht are marked P2? Are these newer Elisco productions?
Have not yet seen the P2 markings.