that would be difficult for most many weapons, and would be different for all of them, Im thinking a much higher skill level required then most mod mags, and would be diffferent for almost all guns, trying to think of how to balance realism with game here, and Im thinking realism is too much hassle to simulate here, so probaly just do it like normal mods, but harder than most things invloving mags.
The internal mags that come to mind are:
tube mags-like pump shotguns, but other weapons do similarly. Don’t think you can extended mag these without being ridiculous as you would either have to change the entire method of feeding ammo in, or extend the tube past the barrel, unless you could figure out some kind of corkscrew feeding method.
true internal mag-basically all your higher caliber rifles, like sniper rifles, seems like there should be a reason for the consistancy of internal, probably a heavy tradeoff on stats especially mobility for increaded weight and bulkiness and a much higher chance of jamming… is that a thing in cata? I’ve not messed with guns enough yet