I have the opportunity to purchase a 10.5" complete upper receiver minus the handguard. My problem is the owner doesn't know the manufacturer and I have no idea how to figure it out. The only marking I can find anywhere on the upper receiver is an "M" on the very front (pictured below). Can anyone identify the manufacturer or let me know where they may be more "clues"? My other question would be, is $300 a fair price for this lightly used upper (less than 1000 rounds)? Thanks guys, I really appreciate it!
I can take different angled photographs if needed.
EDIT ~ No markings on the barrel, only a BOM on the front sight