For the last several reloading sessions, the 550 priming system has been giving me a fit. Reloading several hundred 223 cases over the last month, I experienced numerous instances where the slider bar moves in a very jumpy / erratic movement, fails to pick up a new primer or hangs completely in the retracted position. I tried compressed air, wiping clean the bar and housing, even slowing to a crawl (actually was already there) to manually pull the bar back to pick up a primer and push it into priming position. Another reloader had given me some mica a year ago - tried it too without success. This scenario obviously is not in keeping with the reliability which Dillon's presses are known for. Last night, while educating my 8yo grandson on the facets of reloading, I completely removed the priming system and proceeded to polish all surfaces with 0000 steel wool. I also taught my grandson how steel wool will fly thru the air (while within a magnet's magnetic field). He thoroughly enjoyed the evening's lessons. While examining the bar and housing, I noticed the bar had wear patterns on it as well as a distinct cut that apparently was the result of numerous contacts with the spent primer chute. The housing had a noticible swell just forward of the side where the mounting holes are located. I was displeased to see these wear marks. Anyway, after the through polishing and a final blast from the air compressor, I reassembled the system. The next 300+ rounds were loaded without a hitch. Today, while reloading the last of the now three times reloaded cases, the primer bar was again starting to act in a jumpy manner, not entirely smooth. Two cases needed assistance to pickup primers for loading. I mention this because this press has reloaded tens of thousands of error free ammo. To begin experiencing a problem of this nature is very disappointing. I must admit that the smoothness of the entire press's operation was again very much appreciated, in fact impressive, in the manner of operation when it was running without hiccups. Guess I'll take it apart again and see what it is that I missed the first time around.