Gumboman and PW Burkuta;
The source for the hollow rib was Muzzleloader Builders Supply (as Herb says above).
Thanks PW - yes I counter sunk the holes in the rib so the rivets would have a grip when the heads are flush filed. I'm still doing that, filing the rivets flush, I just do it when I feel I have a bit of time to devote to it.
That rib is
on there, and it isn't coming off without some major event or effort. Riveting is a good way to go in my opinion. I will say that I thought it wouldn't be all that hard to solder the rib on if you tinned the rib lip and prep'd your barrel well.
For the RR pipes I used Stay Brite 8% silver solder (3/32nd dia. 430 degree), tinned both pipe and rib before joining, and I snuck up on the heat gentle like. When I saw the metal just begin to darken to go straw color I removed the heat and waited for the solder to melt.
The pix below shows my soldering setup. The brass shim material you see surrounding the rod going through the pipe is for centering the rod in the pipe, I'll use that when I drill the RR hole too. It was a mistake to leave so much of the shim material on either end of the pipe, tis better to have it all inside the pipe - I had a bit of solder attach to the material and attach to the rib, was a job getting if off. In the pix the blue stuff is wet paper shop towel acting as a heat sink on the other pipe and the tip of the rib where I filled in the end with solder. If I do it again I'll leave that end hollow until after the pipes are on. By the way, the "rod" is actually the RR drill.
All of my technique comes directly from Taylor Sapergia - Thank you Taylor!
dave