This cleaning aid is designed for service rifles chambered in 243 Win, 308 Win, and 30-06 (M1, M1A, and M-14’s). This receiver port inserts into your action and plugs the chamber just like a rod guide. Solvents are prevented from running down into the trigger group and into the bedding. It can also be used as an access port to apply more solvent prior to pulling your brush back through the bore. This receiver port also keeps the bolt in the open position and prevents you from ramming your brush or jag into the bolt face.
Sinclair, Issue:4B, Page:140