Tappet Plate

As the piston nears the end of its forward stroke, it pushes the tappet plate forward, which drives the nozzle into the chamber to seal against the inner barrel and — on most designs — releases a BB from the magazine feed lips into position just as the shot fires.

Tappet plate length and timing are precisely matched to nozzle length and barrel position; a mismatched tappet plate is a common cause of double-feeds, air leaks around the nozzle, or a nozzle that doesn't fully seal before firing. Reinforced polymer or metal tappet plates are a common upgrade alongside a heavier spring, since stock plates can crack under the increased cycling force.

Keeping a spare on hand is common practice among tuners running upgraded springs, since a cracked tappet plate mid-game is a fast, cheap fix if the part is in a pocket but a dead gun for the rest of the day if it isn't.