The name "Valley Forge" was used by two contractors for the Model 1816 musket. The first was Brooke Evans of Philadelphia, PA, who made muskets from 1821-1825. His lockplates are marked with "B. EVANS" and "VALLEY FORGE" ("VALLEY" spelled out) in an oval around an eagle.
William L. Evans of Evansburg, PA, made muskets from 1825 to 1830, so an 1828 musket lockplate should be marked "W.L. EVANS" over an eagle over "V. FORGE" ahead of the hammer; the word "VALLEY" is abbreviated. (Some W.L. Evans muskets have the name spelled "Evens", a stamp maker's error that evidently was thought not worth correcting until a new stamp was made.) A W.L. Evans musket will have the date and U.S. in small characters in two vertical lines behind the hammer.
Some cautions. Valley Forge muskets have been reproduced - the name is an attraction. There is also a great deal of money difference in all those flintlock muskets between an original flintlock and one converted to percussion. The result is that many previously converted to percussion have been "restored" to flintlock, so check very carefully around the touch hole and the lockplate for signs that a percussion bolster was removed and the hole welded up and then drilled for a new touchhole. The signs are there for an experienced collector, but may not be obvious to the untrained eye.
There is no real way I can tell you how to guard absolutely against fakes. The best way is to have seen a number of them and go by general appearance. Parts that look too new, or too good to have been on a military gun issued in the 1830's are a warning sign. So are signs of modern finishing techniques. But something like welding up and re-marking a lockplate may get by even an experienced collector if done well.
Price is one guide. The faker's trick is to ask just enough to not arouse suspicions, while not asking enough to cause the buyer to check. That gun, if authentic, original, and in good shape should go for maybe $2500-3000. If a seller asked, say, $1000, I would be highly suspicious. Also be aware of "cleaned" muskets. A bright barrel after 180 years ain't going to happen unless the gun was in a museum. The ramrod should have a button end; anything else is not right, but ramrods have been reproduced and a good repro is so hard to tell that it is almost not worth worrying about it as long as it looks right.
Trust in the seller is a big factor. If you have dealt with him before or know people who have and say he is OK, that is very important. Also is the question of his own expertise. If he is a small dealer who rarely handles antiques, he might take in and pay top dollar for a fake, not even knowing what it is. In any case, get a solid receipt with a money back guarantee. The guarantee should state exactly what the gun is, like "United States Model 1816 contract musket, made by W.L. Evans of Evansburg, PA in 1828 and in original, unaltered and unrestored condition" and guarantee that if it is not as stated and has not been changed by the buyer, it can be returned for a full refund, including shipping costs, sales tax, etc. within so many days.
HTH
Most of the above info on markings comes from Flayderman and from Robert M. Reilly's United States Martial Flintlocks.
Jim
