The M120 motor is for speed, and will have a hard time pulling and actual M120. Look into the torque motors, like M140+ motors. You will get better trigger response too! I've heard good things about torque motors + high speed gears for trigger response (TR), but you should look up this... There are cheap, but good quality gear sets by modify for $40.
Also, you will need a better, and quieter piston head, or this isn't really a DMR. The power is pretty low too, as my AEG runs and M120, and is perfectly field legal for automatics. You might want to look into M130's, putting you around 450 fps, a speed perfect for single shot DMR's. For an acutal DMR you will need a modified cut off switch, making you only shoot semi. If you can shoot auto, is isn't a DMR, and most fields won't allow guns above 400 fps to shoot fully automatic.
Also, you will need a better, and quieter piston head, or this isn't really a DMR. The power is pretty low too, as my AEG runs and M120, and is perfectly field legal for automatics. You might want to look into M130's, putting you around 450 fps, a speed perfect for single shot DMR's. For an acutal DMR you will need a modified cut off switch, making you only shoot semi. If you can shoot auto, is isn't a DMR, and most fields won't allow guns above 400 fps to shoot fully automatic.