There has to be some difference. Otherwise, the Black Boots would be visiting anyone that owned an AR rifle and AR pistol because the upper from the pistol could be put on the rifle. Maybe the upper is different.....just thinking outloud, I don't know.

They are listed as 'receiver' or 'other', I forget which. I just reciever an 8.5" .300 blackout barrel so I assembled a stripped lower I got for Christmas with a pistol buffer tube. Unfortunately I didn't look at the gas block sizes so I couldn't put it all the way together. I had a 16" upper that I swapped the 8.5" barrel onto after I assembled the lower. The plan is to eventually SBR it, but I can play with it this way until the stamp comes back. I'm using a 12" free float tube that my .30 cal can fits inside of, so it's a little over 16" with the can installed.

Officially, the rules say a stripped lower that was NEVER made up as a rifle can be logged as a "receiver", "other" or "handgun" and built that way. It can even be made into a rifle later, as it is ok to go from handgun to rifle, but not rifle to handgun. Shorthand - once a rifle, always a rifle.

On AR lowers, there is no differentiation as to rifle/handgun as manufactured.

...receivers are noted as receivers on the Fed form 4473 NOT has handgun or long gun.

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Sincerely,

Hobie