Types of ammo and mags.

For each gun there's ammo or mags you can buy.

Different kinds of ammo could give full wall bang or make the gun more powerful
Different mags you can buy can make the gun hold more ammo or give it a faster reload.

For each gun you must buy a new ammo or mag meaning when you buy a certain type of ammo it won't carry on to all guns.

For all GP guns full wall bang cost 10k GP for each gun, for the ammo that gives more power is also 10k GP. For all GP guns faster reload mags cost 8k GP and for a larger mag it costs 9k GP.

For ZP guns, this includes crate guns, coupon guns, and almost all guns related to ZP besides temporary weapons, costs 5k ZP for full wall bang and 5k ZP to make it more powerful.

For ZP guns, this includes crate guns, coupon guns, and almost all guns related to ZP besides temporary weapons, costs 3k ZP for faster reload and 4k ZP for a larger mag.

Keep in mind if you buy it for a M4A1 it will NOT work on another gun and you would be required to buy another one.

For all SMGs GP and ZP adds on 2 bullets with the larger mag.
For all Rifles GP and ZP adds on 2 bullets with the larger mag.
For all Sniper rifles GP and ZP adds on 1 bullet with the larger mag.
For all Pistols GP and ZP adds on 1 bullet with the larger mag.
For all Shotguns GP and ZP adds on 1 bullet with the larger mag.

No two types of the same ammo or mag can be purchased.

5% more damage will be increased with the extra power ammo.
For the speed mag, 10% of the regular time will be taken off.

And yes, these are permanent.