Magazines should only be able to hold certain types of ammunition (that part should be pretty obvious.) some examples:
- Standard Glock magazines should only hold 9 mm NATO ammo (it might also be able to fit lower pressure, and thus less reliable 9 mm Glisenti, 9 mm Parabellum, and higher pressure and thus more wearing 9 mm +P+ cartridges)
- Colt STANAG magazines, which are almost the standard magazines for 5.56 NATO/.223 Remington weapons should only be capable of holding 5.56 NATO/.223 Remington
- Magpull P-Mags, which can replace STANAG magazines in AR style rifles, but may or may not be compatible with all STANAG fed weapons could be used for both .223 Remington/5.56 NATO and for .300 Blackout, if different caliber barrels for ARs are available.
- STANAG style magazines with single stack followers can only be filled with single stack cartridges like .50 Beowulf and 6.5 Grendel (under the assumption that different caliber barrels would be available, if not then just pick one of them) and are only compatible with AR style rifles with bolts too big for .223 Rem and .300 BLK.
- Shot gun shells of almost every gauge come in varying lengths, and some shotguns are compatible with a greater variety of lengths than others. (Possibly more shorter length shells could fit in a magazine tube than longer ones, but this might be difficult to code, especially since shell length wouldn’t make the same difference in box magazines.)
By just replacing the follower, one could convert a double stack STANAG magazine into a single stack magazine or vice versa.
It might make sense to be able to use magazine converters to allow some weapons to use different types of magazines, if they’re both in the same caliber. It might also make sense to be able to modify magazines to be compatible with a different weapon, but if the modifications require extensive cutting and welding, then significant skill should be required for the final product to actually be reliable.
In many places, (including Canada) the capacity of magazines being imported or in civilian ownership is regulated by law, so magazines in civilian locations would have reduced capacity until a player drives out some pins or does some cutting and/or filing to modify it back to full capacity.
Some magazines could also be modified with different baseplates to give properties like an additional light, more gripping surface, slightly higher capacity, more compactness and/or greater melee damage. Some baseplates could also allow the magazine itself to be used as a melee weapon.
However useful these modifications may be, they would come at a cost, especially if done without skill. Each modification done to the magazine is liable to damage it, with the amount and likelihood of damage being decided by the player’s relevant skills.
Other causes of damage to magazines might be from throwing magazines in a quick reload, loading magazines, unloading magazines, leaving magazines loaded, feeding ammunition from magazines, and/or using magazines as melee weapons.
Damage to magazines makes them less reliable, especially if the magazine is filled to a high capacity, and causes a variety of malfunctions, but I would simplify them all to just be failures to feed. A failure to feed can be addressed by simply manually cycling the action until it feeds successfully (though if the magazine is extremely unreliable, it may be wise to replace it or lessen its load before continuing to attempt to feed from it)