A few months ago I purchased my first Handi-Rifle in 45-70, it is a plain Jane 45-70 with a synthetic stock.
With the exception of the trigger, something that I have addressed in another post, I love this rifle.
I also love to shoot smokeless muzzleloaders. The Handi platform with a 1:20 twist makes for a great lightweight carry rifle.
I had thought about buying a second 45-70 barrel and threading the breech for a breechplug, but with access to a machine shop I thought that I could make a "False cartridge" breechplug that would kill two birds with one stone.
The following are some pictures of my trial project:
Left is 45-70 case, right is my breechplug with module.
Once again, left is 45-70 case, right is my breechplug with module
Here we have the 45-70 case on the left, the module in the center, and the breechplug on the right.
The "false cartridge" is made from ampco bronze which is very tough. It is machined to the mirror image of my chamber with the exception that the open end is flared a few thousandths to ensure a very tight fit.
The first shot is done with a mild load and this seats the breechplug so that it is not removable without considerable effort.
The primer is a cut down base of a 45-70 and the primer pocket has been machined out to receive a 209 primer. The hole in the breechplug is 0.031 which prevents excess pressure from reaching the 209 primer, since they are not designed for 40,000 psi. loads.
Another advantage of a 209 is that it is longer than the thickness of the 45-70 head web thickness. This means that the 209 extends through the bottom of the case and adds another level of sealing to the system.
My first few sessions at the range show promise, but I need to work on the trigger before I can be sure how accurate this will be as a muzzleloader. I see no reason that it should not be as accurate as a cartridge rifle, once I find the right load.