What I believe you're describing is called "bump firing" and can be done with most semi-automatic centerfire rifles.
One way to do it:
The gun is held at waist level and the thumb is inserted through the trigger guard and hooked in a pocket.
The gun is then pulled forward with the off hand so that the thumb trips the trigger.
After firing, the recoil drives your rifle back and the pressure of your off-hand pulls it forward again, firing another shot.
Repeat until the rifle stops.
I've seen it done, but never done it myself. It's wasteful and inaccurate, but if it does it for you, have fun.