I really like the H&R single shots. I have a 12 gauge and I have been watching for a .45-70. It seems odd to me that they didn't make the barrels interchangeable. It would have made them very versatile to have one receiver and swap the barrel.As it turns out, Tom, the barrels are interchangeable, with certain caveats. Not like a Thompson Center rifle, but with a little fitting they are easily interchangeable. You've got to use an SB2 frame. Shotgun frames aren't strong enough for some centerfire cartridges. H&R 1871 used to have a service where you could send in your receiver and have new barrels fitted to it. Now that the rifles are made by Remington at the Ilion plant, it's yet to be seen how that service will remain.
However, the folks over at the Greybeards's Outdoors Forum have everything you need to know about the Handi Rifle in their forum. Two of the threads are particularly intersting. The FAQ's thread is a must-read, and the Handi-Basics 101 is also full of information. Those guys at that forum know all there is to know about the Handi-Rifle and they're willing to share the knowledge. Go over and browse around.