Yes they are.
If you add additional parts to make it 922r compliant, yes.
Originally Posted By 223spree:
Who makes 922r complaint parts for the M3?
I believe Geissele makes a hammer for the M4 LINK
, and it looks identical to the hammer on my M3. Might be worth your while to shoot them an e-mail to see if it works
ETA: If you would consider a used M3, the older HK imported M3s came from the factory with a single piece extended mag tube. I saw one a while back for around a grand, but I bought a used beat-to-snot M1 Tac instead to use as a parts donor for my other inertia drive Benellis.
Both my M1 and M3 have 7+1+1 capacity when you ghost load the ninth round.
ETA: HK imported M1 and M3 with factory pistol grips and seven round mag tubes:
The M1 has a two-piece tube, and the M3 is a single piece design.