"Simplest what? Repeating handgun? Automatic rifle? Revolver? Single-shot gun?"
Well, that's part of the question... including parts count.
Even the 1911 has exactly 60 individual parts in it including the staked-In parts like the ejector and the front sight, and the four grip screw studs which are not easily removable without a smith's properly-ground screwdriver.
Sounds like a lot, but the thing can be taken down to just about every single moving part (except the mainspring housing) using no tools but a cartridge rim and the hammer strut in the field.
Now that's simple, from one point of view --as opposed to the "one chunk of metal" the OP mentioned.
So, in this case, "stripping" means pretty much stark nekkid, whereas with some guns you can't get into the firing guts in the field and with some you do need tools like a hex wrench and the like.
So it's all part of the discussion, to my mind.
Terry, 230RN
ETA: That 60 parts included the mag, mag floor plate, spring and follower.