My first guess, and its just a guess not having the P89 in front of me
to examine, is that at some point along the frame's rails and or the
slide's corresponding surfaces, is that some galling has occurred. Is
the gun stainless? My experience with the P series is only with the
stainless variants but this is a fairly rare happening I would think but
not unheard of. I have a Les Baer 1911A1 in .45 Acp that is all stainless
where the Ruger's frames are either aluminum alloy or polymer but I've
not had any galling on either the slide or frame on that 1911A1 but I do
know that Baer crates the slides and frames out of different stainless
alloys specifically to eliminate or hold down drastically, the chance of
galling. I don't know if Ruger's stainless riding on alloy would provide
the kind of friction needed to gall the stainless in the slide or not but I
suppose its possible. Another possible cause might be that either the
receiver's rails or the slide surfaces have somehow gotten dinged up
just enough to create a high point or more along the slide travel but
I imagine you've looked at that closely with a magnifier already, if not
you might wish to do so under a good light.
