4 kg of CO2. That's 2000 liters of gas @1 bar @ roomtemperature. Your ram uses per stroke 27 liters. That means 60 strokes at least(not counting losses due liquid CO2 venting). In a 3 minute fight it's an action every 3 seconds (or 6 if it's double acting)

I would say, use only 1 main storage bottle if size is bothering you.