The problem is with DR. Assault rifles will never be better than snipers for single aimed shot, nor better than BG for burst and this is all for good purpose. So what does Assault have? Single unaimed fast shots, but with people running around with 80% DR and 17 DT, you are lucky to get 20 damage a shot for like 20 AP.
There are a few routes you could take to improve this. Give single shots an armor penetration modifier? If you simple buff the ammo, other guns (PKS and such) will be benefitted as well. If you give the weapon a modifier that reduces DR then the burst may become too strong (burst is still meh).
Reduce AP of assault rifle single shot significantly (without altering aimed shot). The problem now is that you barely get 1:1 damage:ap. So in 5 shots you've done 1/3 of your opponents life without any critical modifiers (knockouts/cripples) for your entire AP bar. This pretty much makes you shit in every 1v1 or team fight. Now if we can find a way to increase this ratio to 1.5:1 or 2:1 then you might have something. As it stands, the damage:cost ratio is fucked