Its your weapon. You cant buy it @ the gun shop, and you don't have to buy upgrades either. It will last, depending on how many shots fired, for at least 50% of the game. There are, i think, 2 golden AK's on each map.
If you want, you can buy a gun case at the gun shop, and put it in there for later. It can be retrieved in any gun shop room, or any unlocked safehouse.
another small correction: The golden AK's will not rust or blow up on you the reliability is 100%, 100% of the time. so you can use it as long as you want. That is why it is a golden AK, if it could breakdown on you it wouldnt be golden.
Originally posted by BioError: another small correction: The golden AK's will not rust or blow up on you the reliability is 100%, 100% of the time. so you can use it as long as you want.
Small correction - no 100% of time, to me - he was broken after more/less 50% of the game.