[Zfurlong]

It's possible the winding mechanism in the drum mag is too strong, I would recommend leaving the winding mech fully compressed for a day or two to settle in (break in), another possibility is that the pressure you are running the hpa through it is too high, solved through regulator, another possible fix is the hammer and hammer spring may need adjusting due to releasing too much gas/hpa at once, another option for too much gas being released is by playing with the screw for the output valve on the mag to get the desired amount of gas released with each shot (bit of trial and error with this one), the last option I can think of offhand without seeing it is the return/recoil spring being too strong, solved through a new weaker spring or leaving it with the slide locked back for a few days to settle in. Hope this helps.