Yes. But only with weapons that consume 1 ammo per shot.
1. Fire one rocket from a full Vladof Launcher (not the Mongol)
2. Merge the rocket to another slot (swap weapons, and during the swap animation open the inventory screen. pick up the launcher in the equipped slots and switch it with the gun that you switched to. *look up Bl2 merging online if you need help with this proccess there are many, many well documented videos and it still works in the latest version on all platforms.)
3. Check the gun you merged it to, it should now cost 1 less ammo per shot. (0 if it is a 1 ammo per shot weapon)
4. Perk of this kind of merge, you can remove the vladof rocket from your equipped weapons and the effect will persist across all weapons - this is also a good idea because if you switch back to the Vladof launcher after performing this merge glitch, the ammo reduction effect will cease.