Bill - thanks for checking and the offer. But I made some good progress today.
The 19/32” (.5938”) reamer I bought off Ebay for $10 arrived yesterday. So today I set the reamer up in the lathe ready to bore the cases. But first I wanted to make sure all the cases I was going to do were the same size at the mouth. A couple weeks ago I was looking around for something I could use to size the case a little bit. Digging through a box of bronze bushings I found one that had a .636” ID. That was perfect! So I slightly polished the entrance to the bushing so it would start on a case. I was able to neck size the case by placing the bushing on the case and running it up through the 7/8” hole in the top of my press, then knocking the case out of the bushing with a dowel.
So I sized the 6 cases I had made before by drilling and another 20 cases, for a total of 26. After I had the necks consistent, I set each one up in the lathe, centered it and then reamed them 1/2” deep.
So I now have 26 cases reamed to .5938”. For the time being I’m using the .590” minie’ balls, so they will be a little loose in the case. But that’s ok for now. The rifle’s groove size is .594”. I want to order a mold from Accurate Molds for a short .595” diameter bullet. After the cases are fired they will expand .001 - .002”, which should result in a case mouth around .595”+/- .001”, which will be perfect for the new bullets. By neck sizing with my bushing, I should be able to get a nice snug fit for the new bullet. Well, that’s my plan. We’ll see how it goes.
This is really an odd and obscure project. I imagine very few of the folks on this forum have any interest in it. But for the few of you who have been following this and offered advice and encouragement, I really appreciate it. It’s pretty unlikely that anyone else will be reloading the .58 Roberts anytime soon. But I hope by documenting what I am doing here on the forum, perhaps in the future someone else will pick up one and search for information. I hope this may be of some help to that person in the future.