Beyond one hex range, a burst turns into a 3-hex wide cone, with the target in the center. So with any burst weapon, once its beyond that one hex, is impossible to my knowledge to hit with every single bullet per burst because of that Spread.
Note 2- Dual-wielding P90s in RT isn't really that special. Probably due to the fact you have to a) wait for the change weapon animation, and b) wait for the APs, and even if you have high enough for that, reason A still stands.
Fighting that way in RT is highly... inefficient, but that is my personal opinion on it, though I am an extensive SG-burster user so I hope that counts for something. :/