The Standard Catalog of Firearms is a useful handbook for identifying gun makes and models. It's far from complete, but it serves as a general guide if you have sufficient experience to make effective use of it. In general, "variations" are not accounted for - This has resulted in some bizarre undervalue situations in the market. Any in particular that you've noted? I'd like to offer the author some errata. My pet peeves: Early LP08 pistols with micro-adjustable sights are worth a premium, but the book doesn't mention the micro-adjusters, only referring to premium value for 1914 dated guns (whereas the micro's extend into 1915). LAR Grizzly variations are not noted, and prices are about 5 years out of date. The Springfield Omega shows no variations, and prices are long out of date. Freedom arms guns - Sold for more than 30 years - Are all but ignored. The entire production of S&W hand ejectors is dealt with in a single entry! Rare variations sell every day for peanuts! The S&W Single Shot variations are ignored, and the price of these guns is severely depressed due to the lack of info. Guns shipped to King's Gunsight Company by the Colt and S&W factory are ignored. These rare and desirable variations command huge premiums. Pricing information for Colt SAA's is practically useless. Ditto for early 1911's. Yes, I am aware that there are entire books devoted to Luger, S&W, Colt, and Ruger variations. Wouldn't references to these books be a grand service?