Will a 7x64 reamer clean up a 7x57 chamber or will the barrel need to be set back?

Yes, it'll clean up, depending.

Ken Waters addressed this procedure in one of his articles; he rechambered a military Mauser 7x57 to 280 Rem, a close cousin of the 7x64.

He found a problem in the neck area; apparently the oversize military 7x57 neck portion was actually larger than the new reamer neck dimension and so the new chamber had a noticable shoulder halfway up its neck. You might wanta make a chamber cast before cutting.

I can find the Waters article if you're interested, I have all the old Wolfe mags.
Regards, Joe

PS just remembered that my Trinidad roommate had his father's Brno 21 that had also been rechambered from 7x57 to 7x64, and apparently had no problems. However this was 1965, the rifle was a full-stock carbine (NOT known for accuracy), we were both young-&-dumb and not really interested in benchrest accuracy, and we never tested the rifle. FWIW, good luck, Joe

There is another problem.

The base diameter of the 7x57 cartridge is greater than that of the 7x64 Brenneke.
So the cases will buldge (if not rupture) under fire in the chamber , if only reamed up.

I know it was done by some smith´s in days gone by, but to my view it´s not a good idea.

Heavenknows is correct. There is also a second problem. The neck diameter of the 7x57 is .320. The neck diameter of the 7x64 is .313. So even if you were able to clean up the base of the chamber you would end up with a step in the neck area. You would have to set the barrel back slightly more than the length of the neck on the 7x57.

There was an article years ago in one of the GUn DIgests about this same problem (don't remember which cartridge). It turned out the accuracy of the rechambered rifle was awful until the author noticed the step. He set back and rechambered and the accuracy improved greatly. I don't know what the mechanism would be, but it is still a bad chamber, no matter where the "bulge" is, so it could happen.

Thanks to all for the valuable information.

chamber cast the 7x57 and put calipers on it .. or set it back a thread, and forget about it

If it's not too late to add a comment...post your thread on the European Hunting Forum. I also asked about this and got some useful comments from those that had do it to 280 Remington.