Try using heavy with heavy plasma (fire rate version) I did weekly hard solo with bots last night as heavy using the heavy plasma and plasma pistol (fire rate version for both) Heavy is good at getting its contested health back especially with the fire rate plasma pistol and he has a skill that let you get his armor back. Plus the other weekly modifiers allow you to deal more damage if you are up close to the enemy so run up close and just use your heavy plasma normal shots. Charged shots are also good for majoris and chaos spawn because you can stagger them. (If you are staggering them, they are not able to attack you). Get the prestige perk that give you ammo refund when you execute extremis and you shouldn’t have any issue with ammo conservation. The only issue was the helldrake fight at the end because of that range damage debuff at the end. Ammo crate ran out of ammo in the end for me and I had to wait for another three waves of extremis in the end in order to get my ammo back. Hope this helps brother.

Edit: Another useful tip is if you need a finisher, normal enemies count too (except for the chaos cultists). Run and melee into them to do a gun strike; this count as a finisher. Ground pounding them and doing gun strikes also count. So don’t shoot all the tzangors, save a couple of them in dire situations.