I have been working on my Qb79
I Bought it converted to HPA already.
Will list my mods in order.
First I polished the tubes with grinding paste followed up by some rubbing compound and washed out followed by a good lube. This smoothed out the cocking action dramatically.
Second mod was to cut the valve spring tensioner to allow better air flow.
Third mod was to enlarge the transfer port to use aquarium tubing instead of that crap one.
Fourth I enlarge the bolt prob.
Fifth I shimed the hammer spring.
I do not have a chronograph yet but as soon as I do will upload the spread sheet.
Next mods will be to add an external adjustable regulator and new stock