John,

Good question. First, what I used as an extension was a ~ 1" piece of another case that went over a new 9.3x72r parent case.

My thoughts were that the extension will be on the outside of the parent case. As the parent case expands during firing, it would press the extension against the chamber & minimize any movement with the extension.

My first effort was merely to use friction but that only resulted in the extension getting stuck in my sizing die.

I then cleaned both the parent and extension cases, fluxed both with Stay Clean and soldered with a high strength, low temperature silver bearing solder (Stay Brite #8. I then sized the extended case and loaded it with 0.5 cc of Bullseye and cream of wheat with wax plug to fireform the case.

Now I have some split cases for vintage rifles that I may see if they can saved for low pressure looads.

FYI: In the past, I had used 1.0 cc of Bullseye with cream of wheat and was plug but split several cases that were fairly undersized for the chamber.

Daryl mentioned brass thin wall brass tubing which he bought at a hobby shop. I remember seeing those at a local mom & pop hardward store (since closed). I saw that these could be bought via the internet and may buy some.