This build is a very difficult one to play and excel with but can be the deciding factor in a fight especially against Teams with Striker and Reclaimer.
I voted for the MDR because you will be dealing Status effects left and right and thus you will get a lot of extra damage from the MDR's special talent.
More of a sidekick to the build I thought that a weapon that can help your teammates heal a bit more might be a good idea in some cases.
You can crit Support Stations and Turrets so shooting at them with your Caddy should grant you team a bit of extra heal.
This will be your actual primary Weapon even in PVP. Only ever swap from it if targets already have the desired status effect or you need to help deal damage.
It will apply bleed and burn and your bliss holster will guarantee disrupt on any targets you can hit reliably which in this case is very easy with the 93R.
You can change this build a bit to run with a different 4-Piece like a Final Measure one but I still prefer to have 50% skill haste in any case.