Ol' Willy
Arcane
I played AR low-crit tincan on hard and true, ammo could be a problem. I used one rifle in 8.6mm and the other in 7.62 and was carrying around 1500-2000 rounds for each. The solution is to employ gas grenades - which raise the damage for every contaminated creature, or raise your critical chance. If you can tank some damage, get closer and your accuracy will improve. Use feats - Suppressive Fire works wonders with Opportunist, put some Concentrated Fire on top to make it even better. ARs are good even without crits.In regular game I never run out of ammo. Combination of convenient traders and ammo drop in enemies/loot. In expeditions in can take more time to get to a single trader in your main base than it takes in regular game to run through all major traders.
If you are tired with traders, just use trader refresh. Life is too short for waiting them to restock.
Also, craft yourself high-quality Biohazard Tungsten armor, with it you will tank both mechanical and bio attacks.