[Xringshooter]

The BATFE classifies things this way:

Long arm (rifle or shotgun)

Handgun (revolvers and pistols)

Other (receivers, frames, and other firearms that are not either handguns or long guns, and NFA firearms)

That's it, according to the BATFE

Everything else is "classified" by the way the trigger mechanism works;

1911 style is a SA pistol
Ruger Blackhawk is a SA revolver
Ruger GP100 is considered a DA revolver (but it can be a SA also)
S&W 5906 is a DA/SA pistol
Glocks, I believe, are considered DA because of the way the striker works
Some newer pistols are considered SA/DA because you cock them and if the round doesn't go off you can pull the trigger again to cock and release the hammer
Other pistols are DAO because you have to pull the trigger to cock and release the hammer for every shot.