If you actually read the MGL, there is no definition for a pistol.
There is a definition for a "firearm". The law explicitly includes SBR's in the category of "firearm".
Don
p.s. to DR Grant's point.
I'm interested in opinions on this process:
Transfer a stripped lower or in the case of something like an MP5, a stripped barreled action. Regardless of barrel length, its not a firearm or rifle per state law. The buyer then submits a form 1.
Once the form 1 is approved the seller then separately provide the parts (This results in a separate transaction, separated by months in time) to the buyer necessary for the buyer to make a functional firearm. Once the buyer assembles a functional firearm, they register it.
If the item in question is coming in from out of state, then possibly have the local FFL hold the balance of the parts while the form 1 is being processed.
MGL for reference.
''Firearm'', a stun gun or a pistol, revolver or other weapon of any description, loaded or unloaded, from which a shot or bullet can be discharged and of which the length of the barrel or barrels is less than 16 inches or 18 inches in the case of a shotgun as originally manufactured; provided, however, that the term firearm shall not include any weapon that is: (i) constructed in a shape that does not resemble a handgun, short-barreled rifle or short-barreled shotgun including, but not limited to, covert weapons that resemble key-chains, pens, cigarette-lighters or cigarette-packages; or (ii) not detectable as a weapon or potential weapon by x-ray machines commonly used at airports or walk- through metal detectors.