The SMGs burst fire says it Hits x3 and it does, but it uses 4 ammo.
I think this is intended, as I believe it is meant to represent poor aim + recoil control. I think the guy you play as isn't John Halo/Helldiver/Call of duty, rather Joe Shmo who woke up here. Granted, if you picked the Soldier, you should be able to shoot 4 and hit 4. Maybe you can find a gun table and be able to add a proper stock, granting the weapon 4x hit and it using 4 bullets. (Not going to lie, using burst fire and having lucky bullet proc, leaving my mag 12/12 after shooting feels wrong to me... But video game logic is video game logic.)