The Infinity or the Extreme Hangin’ Chadd. If you have no qualms about triggering anointment glitches and are invested in the BM tree enough to make sure your magazine is always in good enough shape, an incendiary Lucian’s Call would be an insane assault rifle to use for this. The elemental bonuses from the shield and grenade will glitch out and spawn multiple pellets when they ricochet after critical hits.
Technically it’s up to 100% bonus damage as corrosive. The Handsome Jack test dummy on Sanctuary is weak to fire but also mimics the elemental multipliers of a fleshy enemy. So in TVHM, a fleshy enemy will only sustain 65% of the corrosive damage. This is evident in the video linked above where he fires a non-elemental Infinity which does normal damage, but the green numbers popping up go as high as 6 (which is what would show on screen as 65% of 10 damage per bullet.)
The bonus effect seems way too conditional and contrived to be used outside of one or two gimmicky builds. Compare that to the Blast Master where you get to keep 100% bonus splash damage as long as you don’t reload and is arguably the better bonus of the two. It’s like Gearbox had a brainstorming session and said ‘let’s think of a class mod for Moze that’s intentionally worse than what’s already out there.’ That’s not me asking it to be the absolute best COM and become Moze’s Spiritual Driver, just that Moze can enjoy bigger and better bonuses from other class mods with less time and effort required compared to this new one.
If the bonus escalated up to max after 5 seconds of non-stop firing instead of 10-12 seconds, then it would be a worthwhile class mod for many builds. If I was going to make use of this mod for more general purposes instead of a niche or gimmicky build, I’d say +5 The Iron Bank is the best variation you could get with +24% mag size being the best passive - more mag size and ammo regen is king when it comes to sustained DPS, especially against bosses. And if the special effect is bonus damage only if you hold down M1, then it’s a no-brainer that you need all the extra mag size you can get!