[Jimmy Cao]

IMO a single CIM motor will have plenty of power for what you're doing. A CIM is roughly as powerful as 2 FischerPrices, and it is more resilient to stall/heavy usage. If you don't need any reduction, just direct drive the CIM. A rather small transmission for the CIM that can provide decent reduction would be the DeWalt planetary transmission (see CD Whitepapers, All About Dewalts, if I recall the name properly)

Depending on how your shooter works, a single RS545 (Banebots) might also be enough, geared properly. Banebots sells 4:1, 5:1, 16:1, 20:1, 25:1 (?) 36mm transmissions for this motor. Be careful, however, since these motors do not like being stalled and will heat up rather quickly if they're forced to work hard. They will die on you if overworked.