tri-burst is a waste of money.
learn to bump fire if you can't get legal full auto, this is best done using an AK, and is totally legal
hold the forend stiffly at waist level, hook your right thumb in your right pocket, with your trigger finger straight and stiff, pull the rifle. into your trigger finger.
i'll now get a tirade of "that's poser crap", and "that's not safe" from the usual people on this board., but that's why this is america, YOU decide what's best for you.
you should be able to dump the mag in FA rate with very little practice, and it's fun.
now the disclaimer.
do this when you are TOTALLY sure of your backstop and area around you,as with all FA fire, it's hard to get used to controlling. this can be dangerous if you are not careful.
o.k. guys, flame away.
(edited to add, that while it's fun,it's mostly a waste of ammo and nothing beats the effectiveness of well aimed,fast semi auto fire.)