I've been to Knob Creek and the shoot in Westfield, MA a few times. Each time I try something that I own that has been neutered like the M16, G3, and M1a. It's fun to see how the gun handles compared to the semi-auto version.
Let me be the first to tell you to leave your car running. That's because you will empty that mag so quickly that you'll be finished much faster than you anticipate. After learning just how fast 20 rounds full auto will last, my appreciation of the discipline that soldiers have to have in preserving their ammo during a firefight was exponentially increased. Even with the 3 round burst, you only get 10 pulls on the trigger with a 30 round mag in an M16.
Still, you will get back into your car with a smile that will last most of the afternoon! Oh, and have someone with a video camera off to the side if you can. Record it for the future so you can watch it over and over again. It's not an opportunity you'll get very often.
Have fun!
Rome