Skopia:
Just shot my new .50 cal Disc Extreme today. I used the FPJ plug and Triple 7. I like the FPJ setup on the Disc. I experienced virtually no blowback with that setup.
Not sure what load you're going to use, but I used this one based on the the great advice found on this forum.
Two 777 pellets, Winchester 209 primer, 300 gr. .44 cal Hornady HP/XTP bullets, and Crushed Rib Green Harvester sabots. Boy are those sabots easy to load... Absolute tack driver of a round -- MOA all afternoon at 100 yards, cleaning between every shot.
Have fun -- you'll love this gun.