Pump rod milling?
I think it has been answered before, but I don't even know what to call it so I can't search for it.
CCM guns no longer have the main pump guide rod milled with those three "scallops", or grooves, or whatever you might call them. They looked damn cool, but did they actually provide any function? Were they removed from the machining process to save time? Can they be added upon request?
I always thought they were there to reduce friction at the rod as the hammer spring was engaged to keep things smooth.