Update:
I decided to make a few cartridges, and take them to the range, along with some of the cartridges that came with the rifle. I used a .243 Winchester sizing die to neck down 3 25-06 cases that were originally made from Military 30-06 brass. I ran them into the sizing die a little at a time, until they would chamber snugly in the rifle. After priming, I belled the case mouth just enough to get the bullets started, and dropped 10gr. of Unique into each one. Then I seated a Saeco #243, 85gr gas checked, CR lubed and sized to .244, cast bullet in each of the 3 cases. Smoothed out the case mouth, and headed for the range.
I wasn't really looking for any accuracy, just wanted to see if my case forming method worked. I shot the 3 rounds with the cast bullets at a target that was set up at 25 yards. On the first shot, I was aimed at the target, but just settling in behind the rifle, and brought my finger into the trigger guard to locate the trigger - and the rifle fired. I knew from dry firing it, that the trigger was very light, but got reminded of the care that must be taken with a trigger that light (1lb 4oz. according to my Lyman guage)... The bullet strike was about half an inch left of center, and perfect for elevation. The next two rounds went 1 inch to the right of the first hole, same elevation, and looked like one hole.
I then shot 3 of the rounds that I got with the rifle. They made 1 ragged hole, about 1/2 inch above the 10 ring - still at 25 yards.
Once at home, I found that 2 of the 3 cases that I formed, had split in the neck and shoulder area. So that part of the experiment didn't fare so well! I think it was partly because using the .243 Winchester sizing die moves the shoulder back too far, in order to have the neck long enough to chamber. I am going to anneal the cases before sizing the next round, and see if that resolves the splitting issue.
Today I was getting a bunch of cases ready to go in the wet tumbler, and then go through the process of reforming the neck and shoulder. I deprime all of the cases first, and when I tried to deprime the three cases that I shot from the ammo I got with the rifle - I couldn't! A flashlight showed a tube attached to the base of the cases, at the flash hole, and rising about 2/3 of the way to the shoulder!
I've never run into this, and never read of it anywhere, so I Googled it. Seems there were a few of the old wildcatter's that thought that by putting a tube in the case, to direct the flame from the primer to the top portion of the case, and get the powder to light from the top of the case down, that it would burn more efficiently and maybe just as importantly, not scour the throat with unburnt or still burning powder.
There were a couple of different ways that they put these in the cases, but for now, I'm just not even going to deal with that. I'm going to just reform some more standard brass, and start working up loads.
Oh, and I bought a 6mm Creedmoor sizing die to come a little closer to the correct angle for the shoulder. Haven't used it yet, but it's on the docket.
More to come...
(but knowing how quickly I get to things, it may not be too soon?)