Gen 1:
- Magnetic (early) / screw in (late) reciprocating charging handle.
- Pinned (early) / set screw (late) gas block.
- Single front pivot pin connecting upper/lower, held in place by c clip. Rear is held by recoil spring end plate.
- shorter (13"?) handguard
- ar180b looking lower (more boxy), does not accept beaver tail style grip
- ar180b trigger pins (longer than ar15 pins)
- ar180b style safety (wider than ar15)
Gen 2:
- non reciprocating charging handle (also resulted in corresponding notch on bolt carrier)
- gas block held by set screw plus a c clip that prevents it sliding on the barrel
- front and rear taken down pins retained by the lower.
- longer (15 in?) handguard
- re-shaped lower now accepts beaver tail grips
- ar15 trigger pins
- external bolt release add-on located on left side above safety.
- ar15 safety
Gen 3:
Don't think it got to market before the ban but change is in upper only. There's a youtube video explaining changes over gen 2. A shame we didn't get it because I think it'd be the original design in the perfected form.