Either larger magazines... or bullet belt for 4 ap reloading gizmos.
I had two assault rifles(+2 burst/+ 50 % burst), one costing 11/33, one 16/48 ap per shot/burst. After first round/commando you're left with 21 bullets in the primary and 11 on the alt. If drugged, that's one more burst from small AR and ap/mp to move. Next round you're left with 12 and 11 bullets which is one more burst/commando for a grand total of 33+8=41 ap after reloading and some ap/mp extra. There wasn't much left in range after that, though I think part of the outcome was coming from the fact my char was wearing the heaviest possible armour at all times. Larger magazines may work for builds that want to (perhaps?) stay light on their feet and dart around corners more often, and, of course, have to use some other belt than the bullet one?
To be honest I wouldn't use such an attachment.