I love the paint and finish! Quality stuff all around. The decorations and greek letters are particularly inspired. And great bang for the buck!
These crits are only as a gun person, and may or may not be relevant to what you are making.
1st my fave: Revolver with hose-connector silencer. The only things I don't like with this guy are the two screws up top that keep you from aiming and jam up the Iver-Johnson style top break. I would also remove the screw from the silencer and replace it with a needle or something equivalent for a nice front sight.
2nd: Shotgun with stock removed and replaced with automatic handgun. Pretty cool. The slide is strange and out of place and none of the barrels line up with it considering you turned the tube magazine into a 2nd barrel right?. If it's a kind of raygun thing all I would say is hide the magazine, destroy the slide and add a foregrip. I'm guessing you ripped the foregrip off the shotgun? Modify that and it should still fit pretty good thematically.
3rd: Front half of rifle attached to top of automatic handgun. This one needs the most work. It's got way to much modern stuff, the scope, the automatic slide. Other fundamental problems like the barrels not lining up or that firing the handgun part would wreck the rifle barrel. Honestly for a rifle/carbine kind of approach I think this guy would be better served by cracking the thing back into it's separate halves and putting it back together similar to your shotgun mod.
My biggest piece of advice is to remove the automatics slides and fancy high capacity magazines before doing anything with them. They just don't fit in anything pre-1900 and look too distinctive to not stick out like a sore thumb. And if you leave them there as functional parts, it starts to get pretty strange when barrels don't line up or seem to be 3x the caliber of your rounds.