Common Practice is that Semi-Autos and Single Shots are referred to as Pistols on the Form 4473, and Revolvers have their own check box. However, this is quite stupid. The term Pistol can be used for all handguns, and in the past it was quite common for Pistol to be used referring to revolvers.
Arguing that one is not the other and vice versa is like splitting hairs between a Riding Crop and a Driving Whip. The differences do not matter, don‘t even try to make the argument and being a pedantic jackwagon. 
Because no one should even care. Pistol is as generic a term as “Handgun” and can correctly be used interchangeably.
The 4473 is rife with retrograde thinking. Defining pistol or revolver is just one. Rifle or Shotgun also doesn’t matter. If there has to be any split in type, it should be along the Handgun or Long Gun line. And even there, the line is blurry now with Braced Handguns and SBR’s. I could show you different photos of AR-15’s and it would take the Owner of the gun to tell you which is which. So that’s another thing that needs to be deleted. All the SBS/SBR jackassery that is a part of the National Firearms Act… Which was terrible law making back in 1936 and it’s even worse now.
We have laws and ordinances requiring mufflers on a great many things… but on a firearm it’s illegal, unless you pay 200 Dollars for a TAX STAMP. Something you used to be able to buy from a hardware store for 5 bucks now costs you a Grand, plus 200 bucks, and then you have the asinine wait until His Majesty’s Service deems it’s ready to process your paperwork… average is what, 9 months now? This is beyond retarded. The process for doing a background check to buy a Tactical Shotgun is done pretty much instantly, and if you have a CCW Permit, it’s not even required… and if you don’t pass instantly, the background by law has to be done within 7 days or you can by law go ahead and buy the gun.
But to purchase a bloody muffler – you could have a Baby and start a Family before you get approved for a metal tube with some baffles in it. Never mind you could make a suppressor with stuff most guys have in their garages…. but to buy one requires the Federal Government to deem you worthy and you get to pay 200 dollars for the privilege. Thank you, Sir, may I have another!?!
These laws are utterly useless. They prevent no crime, they serve no purpose. They don’t even make the Feds any money as it requires a whole bunch of people to process everything and at the speed in which they get the job done… if it was a private business doing these transactions, they would be out of business. Well, maybe not – they are selling a product that they don’t have to either buy or produce… selling you a Right. Much like the old Catholics selling Indulgences.
Here’s the deal. We either delete the NFA… Or we make the NFA a Checkbox on the 4473 and they get processed like everything else, all at the same time.