Got your email re your post, and came to this site to check on your query.
It's been years since I've posted that message on this board, and I'm afraid I'm a bit rusty regarding that particular weapon.
Having said that, you write that there is for sale near your home an "1839 Saars percussion, with a 42 inch barrel and in very good shape. I did not see this rife, but this is how it is advertised and also said, it was used at Gettysburg. Give me a fair estimate of its value, and wheather its worth buying?"
Too many unknowns to do so, I'm sorry to say. If you could post photos here (been so long I don't even remember if you can post pics on this site) or email them to me, I'll do what I can. But of course condition, original completeness, and provable provenance re Gettysburg would be major factors in estimating value. And as you write that you haven't even seen the piece, you are at a distinct disadvantage ... not to mention me or anyone else, in estimating its worth.
I note also that Marc Schwalm has posted on this string more than once. Marc is a good friend of mine who lives in Germany, and I respect him very much and value his opinion greatly on such matters. Perhaps he too could help you with an estimated value, if a more complete description of the piece and detailed photos could be provided.
Sorry I can't offer you more help at this time. Best of luck, and I will do what I can if/when you can provide more info.