The A1 barrel is thin and has a slow twist (1:12 or 1:14 I think). The A2 profile is thin under the handguards but thickens from the end of the handguards to the muzzle. Most A2 barrels are 1:7 but others are 1:9 twist. The A2 barrel is, then, a little heavier than the A1 profile.
