I wanted to share a bit of information on my older BC MK1 .25 without internal regulator and Im told the FX royale 500 without internal regulator is the same gun so maybe this will help you guys a bit also. It took a fair amount of time to come up with this so maybe my results will help some of you fellows out there. This information is to show the max ability of this unregulated PCP and how the two pellets act with this gun. My 500 rounds sent over the chrono were to see what the maximum stable FPS for my gun is shooting both pellets the JSB Kings 25.40 grain vs the JSB Kings heavy MKll 33.95. I have been shooting the 25.40 grain pellet for the last year and was interested in testing the heavies to get that great down range energy they produce. I will include a link to my chair gun screen shot for the heavies numbers as I set up the gun complete with a BC that has let me take out a starling at 118 yards with a 8 degree incline (my best shot so far with heavies). From what I have found for my gun is the average FPS at the muzzle for the 25 grain with stability is 909 (46.6 ft.lbs) and for the 38 grain is 818 (50.4 ft.lbs.)! The extreme spread for 33 shots was 16FPS for the heavies and 20 for lighter.That is my shot string starting from 3000 psi to 2400 psi, 33 shots( 3 magazines). As for the accuracy both seem equal, both cut same holes at 25 yards and both can be held to 1/2 group on bag working at it. I can hold a 5/8" group very easy without my best shooting platform. These numbers are working real good for me so far, after set up I went out today and dispatched 12 starlings from 45-65 yards including the long shot above. Hope this information can help anyone with this type of PCP or just shooting at similar speeds and wondering about the different pellets abilities. The heavies sure hold there steam at distance, just plug them in your favorite Ballistics calculator and watch the numbers. All birds drop like stones with this much energy