I've had a P-90 for a number of years. For the past three it has been sitting in the gun cabinet because it was misfiring--i.e., a couple of rounds from each magazine would require two hammer strikes to fire. It has been a while, but I think I recall seeing light firing pin strikes on most/all of the primers.
Is this due to a worn out main spring? If so, is it a DIY job, or should I send it to the factory or take it to a gun smith?
FYI: I have been kind to this gun, firing almost exclusively standard velocity ammo--and only a box or two of +P (although it should be tough enough to take a lot of +P).
Also, my first P-90 was replaced by the factory because it had a rough spot on the bottom of the barrel under the chamber that was grinding away at the frame. This P-90 (the factory replacement) has gone back to the factory as well--for repair of the magazine catch which fell out of the gun at the range.