Weapons trivia. I will point out the facts, I know, concerning this picture and then ask a question I'm unable to answer. This Colt receiver failed inspection, at some point during the machining process, which is why it lacks a serial number or finish, and was demilled, cut in half, with a saw cut behind the magazine well. Had this receiver been complete, it would have been only for law enforcement or export as the receiver lacks "PROPERTY OF U.S. GOVT" marking. I know what an M4 is and what a M16A2 is, but what type of weapon does the marking indicate?
Although it doesn't answer the weapons trivia question, this link contains the only information I've been able to locate regarding the Colt M4/M16A2E weapon.
Weapons trivia. This is a three part weapons trivia.
1. What does the early M14 rifle and the M1 carbine have in common?
The answer to the first trivia question is, the M1 carbine butt plate screw is one of the two butt plate screws used on early M14 rifles. This butt plate screw was originally designed as the "short" butt plate screw for the M1 rifle. So, this "short" butt plate screw was used on M1 rifle butt plates, M1 carbine butt plates, and early M14 rifle butt plates.