Welp, the ammo from Buffalo Arms arrived about an hour ago and it has been an interesting hour. I fired one round with the rifle on the opposite side of a white oak just to make certain it wasn't going to come apart. Everything was fine, paid attention to the bolt opening, examined the brass and all was well. Then to the bench. Fired 3 for group and rifle is about 3 inches high at 50 yards. It might be on or just a tad high at 100 but I didn't check. Then I looked at those 3 rounds. Son-of-a-gun, must have a little headspace issue. Two had the ring that is a sign of incipient head separation and two were fine. I didn't hear or feel anything untoward when firing them but something is evidently amiss.
Being of a curious bent I pulled 3 bullets and weighed the powder charge. 43 grs. of what could be IMR-4895. Now I don't know that, I did say "could be". Only reason for that suspicion is that IMR-4895 is a really popular and common powder for the 8 X 57 and 8 X 56. I dumped a little of my 4895 into my hand and compared them that way and they looked the same but, I've been doing this too flippin' long to not know that a lot of extruded powders are very similar in appearance. Anyway....I dropped two grains from each charge, re-seated the bullets and back to the bench. Hmm...the report and recoil were easily, discernibly different, less. No great shakes but the difference was apparent. Rather than hold center with those 3 rounds I held at 6 O'clock. When checking the target I had a nice, round 1 1/4 inch group that was centered. I didn't set up my bags but kneeled down and leaned against my bench resting my elbows on the bench so I'm not disappointed in the group. The good thing was none of those 3 cases showed an incipient separation ring. Bolt lift was smooth and easy with all rounds fired and all primers showed just the barest beginning of flattening except for the 3 I dropped the powder charge on. They were still nice and round.
Using a sharpened and bent coat hanger I checked the two cases that did show the ring. The place where the ring shows on those cases could be felt with the coat hanger. None of the other cases evidenced any sign.
So, what to do? Easiest and quickest is to pull the remaining bullets and drop the powder charge by 2 grains. I suspect that's what I'll do. Or, I could pull the bullets, neck the cases up to 9mm then set a false shoulder with an 8mm sizing die, fire form them to the chamber and go from there with correct fitting brass. The cases were made using Hornady 35 Whelen brass. If I ever make any, which will obviously be easy to do, when I reset the shoulder setting a false shoulder and fireforming is the obvious thing to do.
Even in the early 1900's chamber dimensions could still be sloppy by today's standards. I know of a few 1908 M/S rifles that will chamber 8 X 57 Mauser ammo. Some could have been re-chambered but I can't believe it would have been done in Europe. They knew the difference between the two cartridges. Even if it's true some were re-chambered it's certain that not all were. Chambers could just be that sloppy back then.
I'm a little disappointed but not dissatisfied. It's an easy thing to accommodate and the rifle shoots pretty good with first try ammo. The ammo also cycles through the rotary magazine like butter...which is quite pleasing....
Now to get the dies here so some real fun can be had!!!