I'd like to work up a load for my M77 tang safety 7x57 and have a mix of Sellier & Bellot and Federal brass. The problem I'm having is that the S&B brass will not fit in the #2 Lee shell holder like the Federal, the rim is too wide. I've got a couple of other shell holders that the rim will fit in but neither hold the brass tight, there is a lot of end play. I don't want to start loading a bunch of rounds only to find that the headspace is wrong, or pull of rims as I'm pulling them out of the dies. Any suggestions?

get new brass, if its too big for the shellholder you could file it down to fit, but its probably not worth the trouble.
RR

That is what I would do. I have seen some odd things with S&B brass (flash hole sizes, etc.).

Definitely get new brass.

You could try an RCBS #2. It is used for 6.5x55 brass that is slightly larger in the rim.

Like trying a RCBS #2, the Lee shell holder is their #3.

When ever I've encountered your problem with a rim I've often used my bench belt sander to deal with the problem.....a quick rotation of the brass rim on the belt does the trick for me.

Have reloaded 7x57 mauser for a number of years now.....one of my favorite rounds to shoot. Don't think I've ever used any Seller&Bellot brass before or their ammo for that matter. Personally, I use a lot of Prvi Partizan brass for reloading. Its decent stuff and reasonably priced at Grafs and Sons.

IIRC there is a rimmed version of the 7x57, are they headstamped "7x57R"?
RR