Having been in the refinishing business for many years as well as doing work for some of the gun companies through our shops, all of the points ,views above ( except for the WD-40 comments) can and will be 'true" ,,,,this happens at times for ALL of the companies, and usually MORE of an issue with the Rugers, as they are "cast" 4140 chrome-moly and the batches made for these castings,MUST be "perfect" or the parts will 'plum' or 'streak as noted above.....nature of the beast...yes, for the MOST part,one must carfeully look at the gun,or the parts as this is a "fault" found all too often in aftermarket ,rebluing by many shops...have to look carefully (inspect) that the gun was NOT "improperly reblued"....
yes, the terminology of the wording for "sand" are all to often twisted, but for the most part,mean the same thing...its their application that changes for the process of the steel making itself, or the casting.......

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dan
NRA Benefactor,PMA