Time for a good bit of polishing then before you install the delrin kit. Make sure the slot is smooth both inside and outside. I use wet and dry wrapped round a dowel to do the inside including the cutouts at the rear or the cylinder. It will also prevent piston seal from being nicked on reassembly. Make sure all particles are out before reassembly. Lube the joints on the arm and free up if too tight. Get some moly (i use moly paste from TBT) on the area where the arm will ride on the cylinder. Polish lightly any scores on the pop up breech. Best take the breech out, its easy. Get some moly on the post of the breech and on the bottom where the arm rides to pop it up. Scores may be shaved pellets if the breech was tight to close and unlubed. Lastly, check the "ears" on the cocking shoe and make sure there are no rough edges on the top that will catch on the underside of the cylinder when it rides in the cocking slot. Good luck