Not really, as I didn't install the debouncing device to change velocity but rather to reduce air wasted per shot. Higher shot count being the goal. I was working on the tune to get it down to just below 20fpe, as the gun came to me shooting just a few shots at about 28fpe and I don't need it anywhere nearly that powerful. Or loud. So I chopped off some hammer spring and added about a 6mm long brass preload shim. Took about 30% off the hammer itself with a grinding burr in a Dremel, carving away behind the head and cutting off the sides and bottom as well, leaving about 1/4 of the circumference in contact plus two small corners about 1mm wide each. Lower friction, more consistency. Lighter hammers seem to work for me in modding my previous PCP carbines, a Brocock Atomic and a 2240, so no reason it wouldn't work out the way I wanted with the QB78. I'm very happy with the tune, but await a Ninja 13ci bottle connector from my friend Rick, a machinist, as I want to put the bottle below the cylinder not in front of it. This is to be a backpack-able take down rifle.

Anyway, at a guess I'd question whether a debouncer would have much effect on velocity. More likely it helps a bit with consistency of air use from shot to shot. As does the 'bstaley mod' - adding O-rings as needed to tune hammer depth of impact on the valve stem. Oh, but my target velocity I should state as being about 700fps with JSB Exact Heavy 18.13gr, or 775fps with JSB 14.39gr, either way being just barely legal per the HFT 20fpe limit.