I guess this shit is still getting worked on even though we haven't heard a peep from the IGAS team in years.
I did exactly the same thing last time I played, those two fully upgraded are beasts, I haven't noticed any difference in damage input between the Blacktail and Red 9, and the former has higher capacity and higher fire rate.I did try the other guns out for full runs but I must of used the Red 9 for at least five years straight. Nowadays I'll use the Handgun or Blacktail.
I did exactly the same thing last time I played, those two fully upgraded are beasts, I haven't noticed any difference in damage input between the Blacktail and Red 9, and the former has higher capacity and higher fire rate.