M4i (Silver) – for specifically ICS CXP/CS4/EBB (include old models) M4/M16 AEG series
M4A (Red) – for Tokyo Marui style (including G&G, KRYTAC, except KWA) Standard M4/M16 AEG series
M4P (Blue) – for HPA PolarStar Engines on standard M4/M16 platform
The MAXX Model CNC Aluminum HopUp Chamber PRO for M4 is the best hopup unit on the market. It has a bottom chamber that prevents BB’s from dropping when switching magazines. It has many extra pieces to allow for perfect hop and accuracy.