Quoted:
Oh, one other thing I forgot to mention earlier... I was using a full 30-rd Magpul clip when I started. By the last few rounds in that clip , I happened to take it out... The remaining rounds were absolutely filthy.
Any chance my Trek requires a "break in period" (for lack of a better phrase) that might explain the blowback and where it might improve? (Or do I need to be on another board to ask that?)
Lastly, can someone explain how the PST actually works? What happens if I shoot unsuppressed with the PST in the suppressed position?
Welcome to shooting suppressors using a direct-impingement system AR !
Yes, the rounds get a lot of carbon them. Even piston guns will have a good bit on them. No way to avoid it. Once again , newer , more modern, more efficient suppressors trap more gas and it has to go somewhere...meaning less out the muzzle and more back down the barrel , out the chamber, in your buffer tube (yes, I know it's a receiver extension), bottom of your magazine, out of the ejection port and into your face.
The PRI CH will help a little but don't expect miracles. Fact of Life: suppressed AR's get DIRTY!
I don't think that your Trek needs any break-in. I 've had blowback in the face from a variety of modern cans on AR's (DI and Piston) , SCAR's. ACR's (using a M4-2000 which smoked my eyes so bad I could not see to shoot for 2-3 minutes) and an AUG. It helps to have a 20mph wind blowing from behind you.
Wearing goggles helps if you learn to not inhale when you feel the recoil.
The PST is a switch that restricts the gas flow back through the DI system. Shooting with the suppressor, you have more back pressure on the gas sytem and do not need as much gas the cycle the DI action. By using the PST, it sends less gas back into the gun giving a milder recoil and less carbon blowback into the rear of the gun. Another benefit is less heat into the bolt carrier area.
Shooting the OBR suppressed and not switching the PST to the reduced gas setting would just give you more recoil, carbon and heat. It's highly unlikely it would damge the gun in any way in the short term. Long term usage may cause a bit more wear and tear on the bolt carrier, buffer, spring and tube.
If you shoot unsupressed thru a PST that is set to suppressed , it will just restrict the gas flow meaning less recoil and gas to operate the system. Bottomline here is that the reduced gas setting, unsuppressed might not cycle the action depending on the ammo.