I cobbled together a homemade bumpfire stock (aka "slide fire") and finally got to test it out last weekend but for the life of me could not get it to actually bump fire. It fired normally just fine but whenever I applied forward pressure to the front rail I could never get my trigger finger to "float" enough to actually reset the trigger.

I'm ready to toss my prototype in the trash and put my regular parts back on, but if it's a simple technique issue, I'll try it again. Any tips?

Yes, bumpfiring is a waste of ammo, and I believe the slide-fire is an expensive gimmick (hence making my own), but I figured it'd still be interesting to try.