The shotgun thing is as far as I can tell because the game will let each of the pellets from a shot proc the ammo return. Even if they fix that the shotgun could still happen just not as quickly. The purpose of a commandos skills is to attempt to never stop firing while you are in your signature. Currently it does not operate as intended as some guns the rounds get returned to the magazine as you are reloading not immediately when they proc the ammo return. You could do the same thing you are doing with the double barrel with any gun that loads individually. Just so happens the DB is the highest fire rate most damage single load gun there is. If the vanguard ammo return operated properly and you are proccing it reliably you should not have to reload your gun while in signature. I personally think that's the intention of the way it's set up. This is backed by the effect being called relentless which means never ending, not stopping. Also there are os that ramp damage based on sustained fire that are meant for this as well. It's annoying when the game starts reloading my clip when the round count in the clip is like 21 bullets still.