Best Diabolo FPS

930 fps work perfect.

I'm at 870fps and they do very well. Haven't tried them any faster because thats basically maxed out for my Dreamline.

My experience with heavier JSB pellets is that they like more speed, 900-950 range.

It depends on your gun. So I would say 850-950.

I have shot the MKII's at up to 930fps with good results out of my Maverick sniper. However, when shooting them at 870 my groups are tighter and it is much easier to shoot better groups.

900- 930 I've had good accuracy I've read that some were able to push them faster with good results too I'm wondering if it just depends on the barrel or twist rate idk

For me, at 870 the shot cycle is smoother and I don't have to "work" as hard at being consistent from shot to shot. My Wildcat mk1 shoots the 33.9's at 800fps and requires little effort on my part to shoot good groups.
It would be interesting to shoot two Mavericks side by side. Both tuned to the same fps with the same pellet but one with 700mm barrel and one with 600mm barrel. Would the 700 be a smoother shot cycle and better groups? Would the 600 be easier for the shooter to control with a quicker cycle and shorter barrel thus better groups?

One of my best shooting PCP guns is a lowly Hatsan Factor RC. It does well with Meisterkugelns at 750 and 850 fps but at 950 they spread out a lot. It does even better with CPHPs, one hole at power setting 1/770 fps and 2/870 fps, but still decent at power setting 3/950+. I shot an Uragan 2 in 22 cal with CPHPs (Not sure if that qualifies as a diabolo with a hollow point...) as the gun was delivered from the factory. I didn't chrono it but they were definitely breaking the sound barrier with a very loud crack. 10 shots into less than dime sized OD hole at 20 yards. I was kind of surprised by the results. No out of round holes. It did not do that well with Meisterkugeln diabolos. The same gun shot five JSB Jumbo Heavy and Monster pellets into holes not much bigger than the pellet diameter at 20 yards.

My lowly First Generation Umarex Gauntlet .25 only cares for the JSB 33.95, putting my other .25s to shame with "out-of-the-box" hole on hole 50-yard accuracy, at a mere 738.9 fps! Tired of the low shot count OEM tank I recently upgraded to a 38L and switched out the 1900psi OEM regulator for a 2200. Chrono'd today, still hole on hole but @ 798.8 fps. FPE jumped from 41 to 48, not too shabby. WM

Diablo type pellets are actually most accurate at about 800fps or even a little slower. The marksmen operating the airguns are more accurate at 850-900fps simply because it trims operator error to an extent.

Back when I was tuning and shooting my .25cal BSA Lonestar, for 100yd groups, 800fps in good conditions is where I saw the best accuracy, actually astoundingly good accuracy. I've noticed the same in .177 and .22cal shooting field target. On the practice line at my first National championship match (Kentucky 2008) I had my AAS400 set up to shoot about 10.3's at 880-890ps. It was shoot decent groups, not stellar, but consistent 1-1.5" groups. It was getting close to refill time, but I was feeling pretty focussed, so I kept shooting. All the sudden i was putting pellet on pellet at 50yds!! Not talking 3-4 shots mind you, but a dozen or more.....Took me "a minute" to put two and two together, but later I shot a chrono string at the lower fill pressure and discovered it was approximately 800fps and less that was punching the same hole like that...not 890fps.

Kinda hard to go wrong with 880 fps