[webtek23]

I own 2 TM MP5's. I just upgraded one with a M100 spring, metal bearings, and shims. It fires, and at the appropriate velocity, however, the sound coming from the gun makes me cringe. It has a much more high pitched noise coming from it, more like a DEEEW, instead of DOOO. Is that normal for this kind of upgrade. It also has problems firing consistantly. Sometimes it will stick back with the spring partially compressed when it failed to fire because I released the trigger too fast. The grinding noise makes me think that something is wrong with the motor placement or even with the gears themselves, however, since they were just shimmed I doubt it. Comments would be great. Keep in mind that the upgrade was done by myself. I have done many other upgrades and have opened my fair share of mechboxes. This particular unit was used though, so there may be a much deeper issue causing the problems.