Between the 8" barrel, small plenum and 3mm ports it tough to break 12 FPE.
I opened all the ports, epoxied the channel around the barrel transfer port, aligned barrel transfer port, bored out plenum and extra 1.5mm, channels in the hammer, peek poppet, polished reg... only got me to 775 fps 13.6 FPE with the 10.34 and 825fps with JSB 8.4 in a decent 26 shot string. Dropped the scope to 1.3" above bore, reduced velocity to 750 with the JSB 8.4 for 30 shots within 1.6%. It's making 1/4" groups at 25 yds and super quiet. Already blooded in with a rat and a hosp, I will be operating in this range for a while, PP750 is great at 10-35 yards.