The butt plate attaches to the end of the stock to provide recoil absorption and a less frictionless surface. It also protects a wooden stock butt from damage.
Ruger 10/22's with synthetic stocks typically come with an integrated butt plate.
A butt plate can be used to increase the length of pull (the length measured from the butt of the stock to the trigger). There are after market adjustable butt plates for the Ruger 10/22.
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