The APS SPB-35 (similar to SPB-45) refillable standard 35g cylinder fires around 150rounds on APS RAM R and S series. The on/off switch is standard at the end. Require R-tube to fit on M4A60 & M4A61 Stock
Rechargeable Cylinder with 35g store capacity, adaptable to R-series, S-series, A-series and B-series, Fit in M4A60 & M4A61 Stock
For refill instruction here. SPB 45\60 Service Diagram here
Diameter 2.5cm x Length 25cm
330g each