"If your FFL is for manufacturing, you can also make your own

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Are you saying that if I have a manufacturers license I can make my own machine gun?
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Edit:
You answered the question in your edit.
I found this on another site:
ARFCOM
"5150rob
In MA you need a "License to Possess a Machine Gun" and in order to get one you need to be either a "Bonafide collector (CLEO's interpretation of what that is) or you need to be a "Certified Firearms Instructor" recognized by the MA Criminal Justice Training council. This license is called a "Green Card" in MA.
I speak from experience because I got mine about 2 years ago and it was a battle. Most Chiefs (not all) dont like to issue them. I am a Firearms Instructor and a Collector and I still had to work at it for about a month before my Chief would budge. Basically if you are not a certifed FI its up to your Chief to make the interpretation if he considers you a "Bona Fide Collector"
This is EXACTLY the case in MA. Years ago it was a little easier to get the "Green Card" but these days CLEOs are a little less likely to give them out. Some MA Chiefs will make you get a C&R license prior to prove you are a collector. Mine did not.
Your best bet is to do what I did. Set up an appointment with your CLEO and meet with him and expain your intentions on why you want your GreenCard (License To Possess A Machine Gun) and tell him its for collectors purposes. When and if he says, No just keep at it for a few months. If your lucky he will issue it to you and if not.... sorry to say your are out of luck in MA for getting MGs.
If he does give it to you, then you can buy a MG and start the transfer process EXACTLY the same way that everyone else does. But your MA dealer will need to see your Green Card and the ATF will need a copy sent along with your F4 ATF transfer paperwork too because they also check state laws as well and if they see that your state (MA) requires a special license and MA does, and you dont have a copy included, then they will not approve it.
Again, I dont know much about anything (my Wife will testify to that. ) and I will admit that, but I went through the ringer 2 years ago to get mine and I know EXACTLY what is involved in getting your MA "License to possess a Machine Gun."
Good luck and let me know of any help I can be to you in this process.
Rob"