I hate to keep asking questions, but I bought this Drilling on Gubroker a couple of weeks ago: https://www.gunbroker.com/item/937002974
It turned out to be really nice and marked "Deutsche Waffenfabrik Georg Knaak, Berlin S.W. 48 Germany" on the rib.I don't have a clue as to the maker. Made in 1929. Extremely nice condition and finish with essentially perfect bores. It turned out to be a lot nicer in person than in the ads.
I told the seller when I purchased it that it was almost certainly a 9.3 x 72. The ad was wrong on both guesses. When I recieved it, I could examine the proofs closely and it was marked 8.8 72. I put a new case in the chamber and it
seemed to fit perfectly. I then slugged the bore with a sized and lubed .365 bullet ( 9 BNH). Almost never got it started but got perfect land and groove (6 groove) impressions. When I measured both with good calipers, It turned out to be a perfectly spec'd 9mm barrel. No doubt about this; no between size maybes. I had heard about this, but in the several vintage 9.3's I have owned I have never run into it. I fireformed a case to the chamber with a good charge, on the off chance it was a 9x70 R Mauser, but the formed case measured exactly to the chamber specs.
My question is, what is the normal practice in this situation? I plan on taking sized cases, neck sizing only in a 9 x ?? die and loading some gas check 9mm bullets to start.The neck will need to be annealed every few shots to keep down splits, but shooting the 9.3's will really raise pressure and there was so much lead squeezed off while slugging that it has to hurt performance. Does this approach sound reasonable?
As an aside, I purchased a Scherping O/U Combination gun from 1920 ( https://www.gunbroker.com/item/937298063
) this evening. It was advertised as a Drilling but was a 12 over 8x57. It looks to be a gun that will clean up well, and the company selling it is only 6o miles from my home. I think it will be an interesting piece.