I found this site through a post in Milsurp After Hours. What a lucky find. I thought I was one of the few numbnutzes around who was crazy about H&R/NEF single-shots.
My first H&R I got in 1966 and still have it. I was aware of accessory barrels when I first got it, but for many years thought I would "wait a while" before I got any. Next thing I knew, H&R was gone. When I bought my first NEF guns, I didn't wait to get accessory rifle and shotgun barrels. I have a bunch of shotguns and several rifles. Many people think of these single-shots as cheap clunkers, but I get a lot of enjoyment out of them. They are inexpensive, reliable, simple, accurate, and they will probably be the last guns they take away from us. I don't know what else you can ask of a gun.
My .45-70 is just the crummy, basic model but will put all the shots through the center of the target with all holes touching. I bought accessory barrels for this in .357 Magnum and .44 Magnum figuring if they take our revolvers away, I can still fire those cartridges through these barrels. I also have a .30-30 rifle and a sort-of fancy .308 made for the Rocky Mountain Elk blah-blah, which someone got tired of and dumped in a gunshop. I got a bargain on that one.
If you are reloading centerfire rounds to shoot in one of these rigs, use small base dies. If you don't, once in a while you could stick an empty in the chamber that the extractor won't pull out.