Hot spots
Which guns are most subject to fakery? The easy answer is, any gun whose value in it’s altered state is substantially more than the same gun in it’s unaltered state plus the cost of alteration. Perhaps the areas that were first subject to the most fakery were Colts, Winchesters, and Lugers, simply because that’s where the dollars were. As collecting interests spread to other fields, so did the scam artists. Today, it seems that if a gun is valued as a collectible beyond its value as a shooter, there’s a possibility of fraud.

One authority offered the theory that guns in the $2,000 to $10,000 value range were those most likely to be faked. The idea was that this was enough to tempt the greedy to go to some extra effort, but that when you get into five figures, the likelihood of eventual expert evaluation and discovery increases dramatically, along with the possibility of being hunted down by an enraged collector who can afford the legal talent to adequately pursue proper redress.
That said there are certain types of guns in various collecting fields that seem to have the reputation of being susceptible to fraud attempts. This is by no means a comprehensive list -- it’s merely some of the examples that have come up in conversation researching this article.

Percussion Colts - One of the most common frauds perpetrated on novice collectors is the passing of reworked, artificially aged & restamped reproductions as originals. In addition, some specific models of particular concern include Walkers and so-called "Wells Fargo" (a misnomer) type Model 1849’s.

Colt Single Action Armies - Colt authority John Kopec estimates that 90% of the Cavalry and Artillery martial models he inspects have been altered in some way. Some have been made from civilian models. Another particularly destructive trend has been the "reconversion" of short barreled artillery models, many of which have significant history in their own right, to 7-1/2" cavalry models. As with the percussion guns, 2nd and 3rd generation Colts and the better grade reproductions such as the Hartford model have been altered to give the appearance of first generation guns. Short barreled ejectorless "Sheriff’s Models" have been made from the standard model SAA’s.

Winchesters -- The old joke is "You’ve got a rare Henry -- yours isn’t engraved." Some knowledgeable experts believe that the vast majority of engraved Henry’s and 1866’s have been engraved in the last 40 years. Other collectors report standard Model 97 and Model 12 shotguns converted to "trench guns".
Another area of concern is with pre-94 Model 70’s in rare calibers. It is reported that some are being made from old factory made barrels, and some with barrels made from scratch. As with Colts, the availability of authentic reproductions of the lever action models raises the possibility of reworked and artificially aged replicas being passed as originals, especially with novice enthusiasts.

Lugers - Some collectors insist that Lugers are the collectible guns most subject to fakery. As in other areas, this can be especially true for models where a relatively simple variation in markings or addition of a stamping can significantly affect value. The National Auto Pistol Collectors Association has been productively active in discussing authenticity and exposing fakes, making membership especially worthwhile for those interested in Lugers or other auto-pistols. With the special emphasis on condition in this field, unattributed restoration seems to be a recurring concern. In addition the creation of "matching" serial number guns from mismatched guns and piles of variously numbered or renumbered parts sometimes seems to be a significant cottage industry.

Smith & Wesson - Rare "Mexican Model" .38 SA 3rd Model variations have been made up from the more common related Model of 1891 -- a process made easier by the fact that some conversion kits were originally offered by the factory, and still surface from time to time. Recently, forged certificates for Registered Magnums have been exposed. Faked Wells Fargo markings on cut barrel Schofields are not uncommon.

Remington - For years, the classic warning has been to watch out for 1890 Single Actions made by cutting the web of the more common 1875 Model. In an interesting reversal, in recent years it has come to light that many of the "suspect" Model 1890’s may have actually been totally legitimate examples of the even more rare Model of 1888. Sorta makes you wonder how many 1888’s have been ruined by "restoring" them to 1875 configuration.

Military - Generally speaking, whenever a martial variation of a civilian model will bring a significant premium, you will find some commercial versions that have been fraudulently reworked into the military pattern. In addition, some recent areas of abuse include -- faked Enfield No. 5 Jungle Carbines (one collector reports an 80% fake rate); early 1911 pistols made to match by stamping numbers on later manufactured parts; Winchester M-1 carbines; Korean re-import M-1 carbines reworked and passed as original WWII guns; and German small arms with WWII waffenampt markings added. Spurious sniper rifles made from more common issue arms also are not uncommon. Interestingly, many military collectors argue that adding a military scope to an issue rifle is a legitimate practice so long as no machining is required to mount the scope.

Double shotguns -- reportedly a fairly rampant abuse by the more skilled fakers is "upgrading" -- taking a field grade or modestly embellished piece and adding engraving, fancier wood, and other special features to pass it as a much more valuable higher grade gun. Yo, Bubba, I gotcher Dianer Grade ratcheer!

Early firearms - Remember that prior to the industrial revolution, firearms were often individual handmade pieces rather than mass produced items. Then consider that the same tools, processes, and skills still exist today, and the potential for abuse becomes apparent. Reconversion of guns which had once been converted from flint to caplock back to "original" flintlock conversion has long been practiced by some, and, like other restoration processes, may be considered acceptable when disclosed. The reconversion process has varying impacts on value -- less harmful on a Kentucky rifle which may be evaluated on its aesthetic qualities as a piece of individual artisanship, than on a military piece valued for it’s historical authenticity. Of course, Mid-Eastern firearms with early ignition systems have been continuously produced for the tourist trade for centuries. It can be hard for any but an expert to tell if a matchlock or miquelet is 300, 100, or 10 years old.

Engraved guns -- Several noted authorities cited this as a special area of concern -- particularly where period attributed engraving is found on an antique gun and doubly especially where the engraving is attributed to a particular famous artist. My personal impression is that the most skillful modern engravers can duplicate the style and quality of any of the great master engravers of the 19th century. Given the high prices original period engraved pieces command, this can be an especially risky field.

Historically attributed guns -- Remember, paper is generally easier to forge than steel. Beware of faked documents. It can be a very good idea to confirm factory letters -- forgeries are known to exist. Pay attention to what the documents actually say (see also "Pieces of History" chapter in the 16th & 17th editions of the "Blue Book of Gun Values"). Another approach has been the restamping of serial numbers on guns to match those of known historical guns.

Casings, holsters and accessories - Wood casings & matching accessories can substantially enhance values, especially with percussion era hand guns, and many authentic guns are found in reproduction casings. When you consider that an authentic capper for a Patterson Colt may break into the five figure value range, the profit motive in fabricating relatively simple accessories is apparent. The boom in Old West holsters seems to have abated just a bit, but the premium that the major "name" makers brought reportedly resulted in phony stamped markings. Finally, there are reports of fake 19th century cardboard pistol boxes being recently manufactured - perhaps not surprising in a market where some rare boxes can bring $1,000 or more.