Anyone know how to explain the bump firing technique?

CS

Two fingers on the trigger, rifle at waist level , rapidly pull on trigger and hold on.

Life, Liberty Etc.. has what they call some "Bumpfire Academy" videos. Heres a link. Just scroll down their page:

http://lifelibertyetc.com/RangeBag.aspx

Stick your thumb through the trigger guard in front of the trigger and hook said thumb in your pocket.  I guess you could use your belt loop if you could talk your wife into sewing on a new belt loop every time you try this.

Left hand goes on foreend and pulls the rifle forward so trigger is pulled against right thumb.  This pulls trigger.  Recoil pushes rifle back, relieving pressure of trigger on thumb.  Continue pulling rifle forward forward with left hand so that cyle repeats.

If you don't  feel up to the risk of buying full auto parts, this is a good way to get your rock-n-roll on.  The accuracy sucks, though.  Make sure you're shooting towards a big, bare hillside.