3 of my 5 Colts showing the difference between models.
Bottom is an HBAR I have mounted a Burris Fullfield. I used this for matches in the late 80's and 90's and will use it often today. For old eyes i mounted a scope and of course put on a very effective cheekpiece.
The next is a 6920 with an Aimpoint mounted. It has a Spectre sling and G-2 light on a Surefire handguard.
The top is a Colt M-4 Carbine with 14.5 barrel and perm Phantom flashider. I'm growing tired of complicated slings and am thing of just using a issue silent sling cut to fit and taped with 9o mph tape.
Note the difference in barrel length. 20, 16. 14.5.