All this conversation that seems to point towards it being legal yet no bids. Hmm. Technically the onus would be on the FFL for selling it to you, would it not...?
It seems like the real sticking point in the legality of this would be the flash hider (or is it a "booster") combined with the pistol grip. One or the other is ok - but not both together.
That is why I was curious if this was covered under some sort of C&R provisions. The receiver is new manufacture - which probably rules out the C&R angle - but the rest of the components are old from all I have been able to read up on these.
Also the "booster" appears to be the device just before the cone at the end of the barrel that has holes around it's circumference. I have seen the cone referred to as a flash hider - although I have also seen a few videos of these on Youtube -and they still have a pretty prominent flash when firing. So if it's a flash hider - it isn't hiding much.
I have seen kits for building these and a few completed one's for sale over the last year or so. I have somewhat of an interest in getting one - but I wanted to try and figure out if it was MA compliant. I haven't seen any dealers in MA selling anything like this - I bet a dealer from outside MA probably isn't going to care much about MA regulations - since this will have to get shipped to an FFL inside MA.