I know that, for the ego's, this is a problem, the vibration of the gun cycling was causing the screws to back out. They solved this on the geo (when releasing the G2 kit) by locktite'ing a small patch on the screw, think nylon threaded screws.
I dont, and will never claim to, know anything about the P/DM line of guns, but maybe a small amount of locktite could help?
I'm sure that if I'm wrong, I will get flamed to death.
Dave