I am very interested in underhammer rifles and pistols. My neighbor who used to own one (a 45. H&A), said they were really accurate, and just pretty nifty overall. I was curious about this particular kit, and if it was worth the money, or a good entry level gun, or not. I want to put together a kit anyhow as a DIY project, and this item caught my eye. It might pay off just to keep my eyes peeled for a used H&A. Here's the kit anyhow, you may have seen it. I'm pretty green when it comes to BP.
http://www.longrifles-pr.com/underhammer.shtml
http://www.longrifles-pr.com/underhammer.shtml