Part Number: 304W This brass washer is placed on top of the powders charge bar.Its keeps powders like W296 from leaking from between the bar & measure. If damaged/flattened, this washer can move with the bar. This can cause powder not to drop correctly, resulting in a light powder charge/wad stuck in the barrel. Set the wad seating ram to show a tiny amount of wad pressure on seating. This will show you if there is enough powder in the case. The measure body & charge bar may have to much clearance letting the washer get pinched when bar moves back and forth. Forcing it will flatten the high points on the washer. Then washer will block the powder drop, resulting in a light powder charge. After taking measurement of my 4 Mec 600JR, i found a new measure body was needed. Mec exchanged the old for new. There is also a lot of variation in the height of the charge bars.