A1 vs. A2 front sight base

[sonrider657]

There is a noticeable difference between the A1 FSB on my old pencil barrel Colt than on the A2 FSB on my carbines.
They "look" basically the same but the A1 seems thinner.
What changed?

[Robb Jensen]

There is a noticeable difference between the A1 FSB on my old pencil barrel Colt than on the A2 FSB on my carbines.
They "look" basically the same but the A1 seems thinner.
What changed?

There is a difference between a rifle with an A1 or 8/3 marked A2 rear sight and a carbine with a 6/3 marked rear sight. The front sight bases are about .040" different in tallness. Probably not detectable by the naked eye.

[CAR-AR-M16]

The opening for the barrel is different also. IIRC the barrel diameter for the A1 is .625" and the A2 is .750".