For a firearm to be designated a MSSA it has to fulfill one of the following criteria:
Folding or Telescopic Butt
Magazine of more than 15 rounds for .22 rimfire or more than 7 rounds all others (shotgun included)
Bayonet lug
Free standing 'military style' pistol grip
Flash Suppressor (Sound Suppressors and Muzzle Brakes don't count)
This is in addition to it being a semi-automatic, obviously.
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