Create ammo is a technique a Gangster begins with in Slash'EM Extended. It can also be learned by a pokemon that has gained enough level-ups to reach experience level 15. Zyborgs can randomly learn this technique upon leveling up, and binders with expert firearms skill automatically learn it.
Using this technique causes the player character to "make some ammo for your gun", adding (techlevel+1) bullets to the inventory; if the knapsack is full (52 items or more in main inventory), ammo creation is aborted. This means it's probably a good idea to free up some item slots for using this technique, as every bullet has its own chance of being blessed, cursed or having a random positive or negative enchantment. After it has been used, the player has to wait a random time in order to use it again; the timeout is usually around 500 turns.
A gunslinger player may want to use this technique a lot in order to always have some ammo for his guns; it's only useful for guns that use normal bullets, though. The maximum amount of bullets per use is 31 for a gangster that is at experience level 30.