Put in some faster ratio gears!(SHS 13:1) Couple that with a great motor, and you will be in the clear at 25-30rps
Or go ballz out and make a DSG build.
Just for reference though,
I have an m249 that shoots at 50rps
and
I have a Dragunov that shoots semi auto....
and they both get the same amount of kills!
All my field guns are between 15-25/7 rps, it really is the hop that makes all the difference. I would rather have one mag with a superbly tuned hopup, than 400 shots in a hose.