[Threshold]

You should be using ResetPlayerWeapons before using GivePlayerWeapon. This way, ammo won't be stacked, eventually giving you unlimited (negative) ammo.

EDIT:
Similar situation: https://sampforum.blast.hk/showthread.php?pid=2690150#pid2690150

EDIT #2:
I just realised that the guy's problem was still existant after he did a SafeResetPlayerWeapons, but nobody ever helped him... oh well.