Dry Fire Without Damaging Your Firearm
Snap caps are great for dry fire practice because they let you concentrate on keeping the firearm steady during the trigger pull, which helps eliminate flinch when using live ammo. Shotgun snap caps feature a wool chamber mop that can be soaked with gun oil or preservative to prevent a rusty chamber during long-term storage; available in your choice of a brass or aluminum base.
Big Book Catalog, Issue:70, Page:367
SPECS: Shotgun- Brass or aluminum base, brass "primer" insert, wool mop, 2 3/4" (7cm) long.