In Ma it is legal to build one,
I believe it is different with a SOT than an Individual/trust. Class 3 SOT is a NFA dealer correct? And I believe a Class 2 is a manufacturer?
If you do it as an individual you just get the receiver you want, apply for the NFA tax stamp, pay your $200 and wait and then get it engraved to NFA standards. It takes however long it takes. Mine took 60 business days for a trust.You do not need permission from your police Chief, you do notify whoever you use as a cleo once the paperwork is approved. (Cleo= certified law enforcement officer) You just send their copy to them it is notification you built it only.
Only the Receiver gets registered and depending on the type of gun you can have different uppers for it which is nice. If it’s like an MP5 for instance the receiver is the upper with the barrel but an AR you could have multiple uppers in different calibers and lengths. You still need to abide by the AWB so fixed stock and pinned muzzle most likely unless you are a SOT building it to sell you may be allowed vs a regular person..
I think a class3 you can only sell NFA items not manufacture them.
If you are a Class 2 SOT/manufacturer I believe you just “manufacture” it and then notify the ATF that you made it. There are plenty of dealers on here who i’m sure will chime in.
I just got two SBR stamps back as a trust in the last 4 days but that’s not as a Class3 dealer.
Edited: In Ma and for my fat finger spelling.