Compulsive Reloader, Extended Mag, Chill Clip on Deliverance or Riptide. Blast your 2 shots to freeze then reload and repeat. Also as you mentioned Reservoir Burst. Surprisingly... Compulsive Reload has yet to drop on a Shotgun and I imagine if one ever happened with Compulsive + Dual Loader it'd be kinda nuts. Also, any Suros Synergy weapon in PvP for extra flinch reduction and handling, so your Cantata-57 HC and Fugue-55 Sniper + Box Breathing, Syncopation-53 Pulse, etc. And any Omolon weapon which has the same Top-Half Reload Trait that stacks with it although that's just Snorri atm. It has it's places, but is more situational.