Use this build to both push forward and fallback.
Option 1. Throw the blast-mobile-cover out front, ideally positioned so that multiple enemies are in front. If you can, pull the pin to blast and hammer them with head shots using the MDR. You'll get massive damage from both the blast (125.5K DMG) and the MDR buff (18%) during status effects. This build is low health so if you get rushed by others then pull out the shield and destroy them with head shots. You will be fairly tough with the shield health at about 500K while having 30% DMG resist and 20% DMG bonus.
Option 2. If you can't position the cover to blast, then put it out front, do a cover to cover move into it and use the historian. The cover will have about 840K health with 20% weapon resist. If enemies come over blast them with the shield and use the MDR while they stand around eating your head shots. DON'T activate the shied in preparation because if you blast you want to stand there with the MDR. If there's anyone left and you get rushed pull out the shield and fall back.
You should have about FA:8200 and ELE:5000. With all the haste gear mods the shield cool down will be under 20 seconds and the cover will be about 30 seconds. The MDR has determined on it so when you blast the cover you will have a new blast shield in short order.
* I originally tried the Bliss holster with Decisive Gloves and Sentry, but this 6 piece is far better IMHO.
* The MDR having Determined on it makes it very useful for a Firecrest build too. So if you only have one MDR then put Determined on it and get two really fun builds out of it.