the velocities you quote almost makes me think you are mixing calibers. Ain't no way a .22 is shooting Superdomes at 840 fps. I currently have 3 of them. 2 in .22 and one in .177. Both the .22's are tuned, although to different levels. One is shooting 14.3 Premiers at 710 fps and the other is shooting the same pellet at 690 fps. The .177 shoots 7.9 Premiers at 860 fps and is a Theoben ram that I installed and tweaked. The older .22 is a mk 1 without a muzzle brake, and the other one is a mk2 with factory brake. In my own experience of tuning these guns,when you start to push the gun over 16 ft/lbs, you are in danger of blowing out the rear rotary breech seal. Regards, Russ