rpetrone

Sounds like you are trying to shoot fast splits, but are not tracking the sight properly. Shooting fast double taps requires a gun set up properly for the load. This means you need to try different recoil and or mainspring combinations to get the sight to track smoothly and consistently. Your grip also determines how well the gun will track. The grip pressure should be roughly 60% with the support hand and 40% with the strong hand. Make sure you are not squeezing the grip on your second shot in anticipation of the recoil. This would cause shots low and left in the C ring for a right handed shooter. Double taps are a misnomer. You are not simply slapping the trigger, you are seeing the sight picture, even if it is a "flash sight picture" for two separate shots. To improve my sight tracking technique, I would do "Bill Drills" at 7, 10, and 15 yards. The varying distances will determine how much sight picture is required for the given distance.

Did you crown the muzzle after you cut the barrel? If not, do you think it may improve accuracy?

Not all mag catches are created equal! The mag catch ledge may be thicker than others, which may make the magazine a tighter fit. In fact, EGW sells and oversized mag catch, which pushes the mag higher up in the frame, which can sometimes help to prevent nosedives when the first round feeds. I recently purchased Wilson 10round ETM 9mm mags, and they fit perfectly in my Colt. Glad you figured out the problem and fixed it!

I use my Dillon media separator. I throw the dirt and brass in, close the cage, and crank a few revolutions. Hopefully the rocks you mentioned aren't too big, because small ones will be removed. I then throw the brass in my vibratory case cleaner, add the crushed walnut media, and clean.