Civilian ownership of automatic machine guns has been tightly controlled by the federal government since 1934. Semi-automatic firearms that fire one bullet with each separate trigger pull are readily available and are the most common type of rifle. A Ruger 10/22 fires the .22LR, and its magazine holds 10 rounds, with one extra in the chamber. Extended magazines that hold up to 30 rounds are available. Mechanical modifications to turn it into an automatic rifle is a federal felony, but using a rubber band to simulate the feel of an automatic by bump firing, or pulling the trigger forward faster than it normally would travel, is legal.
Place an extended magazine into the well just in front of the trigger housing.
Place one end of the rubber band on the back of the trigger and pull it forward around the extended magazine. The band should keep tension on the trigger, pulling it forward.
Raise the rifle to your shoulder and fire normally. Leave your finger in the firing postion and pull the rifle away from you with the left hand. The trigger should snap back immediately, allowing the trigger to be forced back into the firing postion by the pressure of it being pressed against your finger.
Tips
Most ranges ban bump firing.
Warnings
It's easy to lose control of a bump-fired rifle and send bullets in directions where you don't want them to go. Bump firing should be reserved for where you have adequate space and backstops.