identifying a colt ar-15

[dakotasin]

local gun shop has a colt ar-15 on the wall - it is a colt lightweight target, or somesuch. the lower is clearly marked 'colt', but how do i identify a colt upper receiver assembly? the gun is an a-2 configuration.

if it is truly a colt, i think i will pick it up ($1200), but if it is not a colt, the bushmaster m-4 next to it does not appear to be a bad deal at $900...

 

[rcmodel]

The barrel will be marked C MP or some variation of that near the muzzle.
C= Colt
MP = Magnetic Particle inspected.

Barrel marks you might find:
Colt C MP 5.56mm NATO 1/7 HBAR
Colt C MP 5.56mm NATO 1/9 HBAR
Colt C MP 5.56mm NATO 1/12 "Chrome Bore" M16A1
Colt C MP 5.56mm NATO 1/7 M4

There would also be C MP stamped on the carrier & possibly the bolt I think.

rc