The differences between an A1 and A2 are as follows:
The A1 has a lightweight barrel with a 1:12 inch twist, the A2 has a barrel that is heavy contour in front of handguards and is 1:7 inch twist.
The A1 has a "bird cage type" flash hider that has slots all the way around, the A2 has a "compensator" (although BATF rules it a flash hider) that is closed at the bottom to prevent dust signature when firing from the prone position. The A1 flash hider is locked in place by a lock washer, the A2 "compensator" is looked in place by a "peel washer" (this device is like a wafer, you peel layers of it off so it's the right thickness so that the solid bottom of the compensator faces down when it's screwed to the end of the threads and torqued to the right specification."
The A1 has a round front sight post with five detents for adjustment, the A2 has a square front sight post with four detents for adjustment.
The A1 has triangular handguards and the A2 has round handguards.
The A1 has a rear sight that is only adjustable for windage. The windage adjustments require a tool (nail, bullet tip, sight tool) to adjust. The rear sight aperature is stepped so that by flipping to the "L" marked long range one you increase the battlesight from 250 meters to 375 meters. The A2 rear sight is adjustable for both windage and elevation. It also has two aperatures, a long range and a 0-2 (0-200 meter) ghost ring type sight. The elevation wheel on the rear sight will allow you to dial in ranges from 300 to 800 meters. The standard battlesight is 300 meters.
The A2 lower receiver has reinforcement in the rear where the extension tube screws into it. It is also roll marked safe and fire on both sides of the receiver near the selector.
The A2 pistol grip has a finger swell in it, the A1 doesn't.
The A2 buttstock is 5/8 inch longer then the A1 buttstock.
Many commercial AR15s are neither A1s or A2s but have features of both. True A2 countour barrels are rare on commercial rifles, most have a barrel that's heavy from muzzle to breech. The triangular handguards are getting rare, just about everyone uses round ones on all their rifles now, including the military.
Since true A1s and A2s have 20" barrels, the 16 inch Bushmaster you are looking at probably doesn't have all of these features and A2 may only refer to the sights and barrel contour and twist rate.
You are the only person that can decide if the A2 is worth the extra money. Think about what kind of shooting you intend on doing. If you are going to use the rifle in DCM competition or shoot longer ranges with the iron sights, then by all means buy an A2. If the rifles' primary use will be home defense, police patrol work or 3 gun tactical match competition, then you may be better served by the A1. It's lighter and the sights won't get jarred off of zero. For this type of shooting you will most likely zero once and never adjust your iron sights again.
If you intend to shoot the heavier 62 grain and up ammo, you will need the faster twist of the A2 barrel. You can shoot the lighter bullets (except for some of the very light weight 40 gr varmint bullets in twists up to 1:7 without any problem. You can't shoot the heavier bullets in the slower twist barrels though. It is perfectly safe to do so, but you will have unsatisfactory accuracy.
So the call is yours, what kind of use do you propose for your AR15?
HTH
Jeff
