Handguns --yes. one of the forms filled out for HG purchase in PA goes to the State Police and is kept IIRC ---in fact circumspect registration. I was under the impression (not sure where I heard it) that a lawsuit was pending in federal court to stop the practice and have the existing records destroyed.
hand guns purchased outside PA,prior to PA residence or without the benefit of a dealer transfer (and therfore illegal) would not be recorded however, for whatever thats worth. The couple of handguns I have aquired since moving to PA I was told by the dealers to keep the state form --not with the gun for some reason--always, even if I disposed of or transfered the firearm.
Also the subject of the warrant may have owned classIII firearms and therefore a registry would have existed for them.