That's a subject I constantly struggle with. I tend to use historical examples for inspiration without making a copy of an existing gun. A lot of times there is a question in my mind on whether I have produced something that could have come out of such and such a shop, or have I just created a mish mash of stolen details? There is a fine line there, but just where does it occur? Is a fantasy rifle something that is totally thought up by the builder, or is it something similar to existing works and possibly could have come from say, the Dickert shop? There are degrees of that also. A builder can easily produce a piece that may not be totally historically correct, but does that mean that it is wrong; and just who makes that decision?
Another area I see in historical correctness is the level of craftsmanship. This is not a criticism of those who are capable of producing a "Super Gun" and doesn't really affect me so much because I don't have the patience/ability to produce one of that level, so I settle for the "workmanlike manner", which is maybe a cop out for not taking the extra time and effort to really produce a top tier rifle, but I can take solice in the fact that a lot of the old guns were nowhere near some of the stuff produced today. Granted that some carving has not survived 200 years or so in unblemished condition, so it is difficult to tell, but there are still some tool marks that are discernable even today, and engraving on a lot of existing guns is something that would be unacceptable in today's world. Where do you draw that line ? I don't know. I am satisfied that what I build will give the user the experience of an 18th century gun, which is really my goal to begin with.
Personally, I have always liked the Beck rifle that you recently created, with the exception of that bent trigger guard. I have often wondered on seeing that piece if the double triggers were a backfit and the original guard were modified to fit. I would not use that little detail on anything I ever produced because it just seems so incongruous with the rest of the rifle. I do realize that it is a documented copy and that is why it is like that, but that raises the question that if you intend to build a copy, do you copy the mistakes also (if that could really be called a mistake)? This also raises the point that I have never seen a copy that when placed alongside the original, that something somewhere was just not quite the same. It may be very subtle, such as the countour of the lock plate or a slightly different size of a screw, but the difference is there.
I suppose it could be argued that none of the stuff we build today is really historical because we use machined steel barrels, cast steel locks and investment cast furniture, all while working under electric light and air conditioning.
All this has made my head hurt.....I'm going back out to my shop.