The 5.56 NATO / .223 Receiver Saver Hammer Drop Block is made of a shock-absorbing plastic. When in place the block prevents the hammer from striking the wall of the magazine well.
The Receiver Saver fits into the magazine well with the upper receiver open or removed and locks in place with the mag release catch. The top is serrated so you can hold it in a receiver that is not fully assembled.
Designed to withstand thousands of hammer strikes and is covered by the Wisconsin Trigger Company Transferable Lifetime Guarantee.