The M8 is the XM8. X stands for experimental I think. (just guess)
Try cleaning your barrel and re-installing your hop up. You may have a faulty bucking. Take out your gearbox and see if there is plenty of air coming out the nozzle.
I would just ask airsplat if they can replace it unless it is a simple fix. If it is something replacing parts or fixing the gun, send it in.