Umarex HDR68 Shorty Powertest 750 psi 59 Joules - 1100 psi 61 Joules 

very interesting results wow we got from 1100 psi and the 9.2g Ammo 6 slugs and no barrel extension 53 joules, and with the 12g Devil Spikes we got 61 joules
with 750 psi and one barrel extension we got 55 joules with 9.2g Ammo 6 slugs and 59 joules with the 12g devil spikes, adding barrels gives huge increases in power