Investing heavily into BM for Iron Bank, Matched Set (with 2 other Torgue weapons equipped) and a 40% magazine size artifact, gives me 2 rounds in the magazine. With Forge and MoD you can basically keep a couple rounds in there at all times, though occasionally it seems to bug out and nothing procs and Forge stops working altogether. Still does massive damage with a Blast Master COM (and hurts you a lot with even a 5% bullet reflect… ugh). You’re extremely squishy, though, so you definitely need to keep spamming grenades in between shots for heals. Very much a risk vs reward playstyle.
Funny side note, the huge extra ammo capacity bugged out my Laser-Sploder. Normally it has around a 21 magazine size, but the display got stuck at 13 rounds for some reason, but would never drop below 12 when I was firing.