If you have a leak from the LPR set screw, then one of the outer LPR orings near the set screw is bad. It may not look bad but swap them out anyway.
A leaky LPR will not be able to maintain enough pressure to cycle the gun.
Make sure you don't have the front on/off knob in the off position as well.
Etek 3LT grey/black f/s
Valken Proton greyish/black f/s
68 4500 PE stubby, LP output f/s
68 4500 AIR tank(no reg) f/s
Creed Battery, eyes and noid f/s