You can try using NVSE, i'm not 100% on the kind of scripts you can make for guns, well your situation anyways.
http://fose.silverlock.org/fose_command_doc.html
That's a list of things the New Vegas Script Extender can perform, not sure it can help but its worth a shot, might provide an alternate.
On another note, is there not a way to already just change how many bullets it restores?
To edit the textures of ANYTHING, you need a .nif and .dds of the object you are editing, I did it with vault doors. You set up the file structure in your data folder, and you point the object you create in GECK to look in that file structure.
When your testing it, if it crashes your game when trying to use it, possibly missing / corrupted .dds, If anything on the gun, or the whole thing is pink, that means its missing its texture.
Edit: Here is the tutorial for the vault doors: http://www.youtube.com/watch?v=RMjnr0C1RTI
I know it's not for a gun, but its essentially the same thing, it still requires a .dds and a .nif for its mesh / texture.