If I've missed a posted answer already, my apologies.
Has the QB HDD been tested on a HPA system yet?
I've got a few QB's I'd like to equip and one of them is dedicated HPA with the other one part time HPA. Output pressure is in the 950psi range so these are not hot rods.
My experience with the Crosman HDD are that on HPA, they do much the same as on CO2 and I've had good luck with them.... just double checking on the QB variant before purchase.
...as well (or even better) than CO2 and HDDs because the lower density and higher flow rate of lighter air vs heavier CO2 makes hammer bounce suppression even more important to good efficiency.