Longrifles are going the way of 95% of the other American antiques, down. If you watch Antiques Roadshow on TV, they commonly re-do a show from 15 or 20 years ago, showing the item and it's appraisal at that time. Then they show the updated appraisal, today. In most cases the item is down by 20-50%. That can be for a $20,000 artwork, or a $400 colonial mug...almost all are down.
I went to an estate sale a couple months ago, the guy was a bigtime early American Pewter collector. Chargers, tankards, whale oil lamps abounded. They were selling most items for $7 a piece. SEVEN dollars. Sure, it was an estate sale, they had to sell it all in one day. I bought 10 items, and came home to research the going rate. Most were about $30-50 in value.
Great gain you say? But not for the original owner - I also found his purchase ledger records, each item carefully documented. Most items he'd bought back in the 60s and 70s and most for at least $150. Some were $300 or more. ALL of these sold for under $50, most for $7. His estate was in the hole by the tune of thousands or 10s of thousands of dollars for his lifetime Pewter collection. He paid enought to have bought a house back then, the market today paid enough to buy a cheap bicycle.