Seems i found me a funny glitch, as long as you hold down the fire button you can have the rate of fire of the current gun switch over too the others
for example shoot with the uzi and while shooting switch to shotgun and you get uzi rate of fire with shotgun dmg.
For those who still trying to beat the last boss i recommend using the pulse.
after experimenting all weapons( everything maxed ) on the last boss I found that the pulse has the best damage per shot on the boss.
best weapons in order for last boss.
1. Pulse ( as long as you hit all shots you'll take out at east 10% to 20% of the boss health per rotation(what ever the boss is shooting best hope is the missiles rotation since its so easy to dodge those))
2. Acid gun (stay close since your range isn't that good acid dot takes care of boss health while your busy dodging)
3. Bullets( stay at the bottom of the screen as much as possible for max dmg, since the combined dmg from all the split bullets exceeds that of the normal shots)
4. Lasers side lasers does all the work for you
999.missiles(if your masochist use this to beat the last boss the dps output of this weapon is utterly useless)