I have tuned some PCP's, and it's not that much different from tuning a springer in some ways. Although not nearly as big, there is a "main spring", actually a hammer spring, and the hammer or striker is somewhat similar to the piston. And of course there's the tube the hammer slides in, which is similar to a springers compression tube. All these parts can benefit from some polishing, deburring, and lubing, same as a springer. But it really depends on the gun. I've worked on the lower end guns, a BAM B-50, a couple of Air Force Talons, and my Hammerli Pneuma. But I never felt the need to do anything to my better guns like my AA's, FX, and my latest, the Evanix Renegade. I'd say this is a case of if it works, don't fix it ;-)! Later.
Dave