You are replacing both of the o-rings on the Sidewinder piston with the correct size *and* durometer, right? If not, I have some o-rings I can send over. They're buna (which I'm sure I'll hear about from someone at AKA), but they'll work.
Originally Posted by Forsaken_id
I'm not sure, but maybe you need a new reg core. It's the part with the reg seat that you adjust in and out to change the velocity.
If the reg core were bad, it would likely overpressurize. If it's not overpressurizing, he should be fine.