I have run across some WW Roberts brass that will not fit my shellholder. Upon examination I found the diameter of the extractor groove to be larger than the brass that fits. This is pre +P brass FYI, was the groove diameter larger on early brass and later standardized? Anyone else encounter this situation?

Nope. All mine has had the same case head as 7mm Mauser, 30-06, 45ACP, etc.

You failed to understand the question, I'm not talking about the case head diameter which is the same. What I am talking about is the diameter at the bottom of the extractor groove. the cases that will not fit my shellholder have a larger diameter here.

One of my reloading books had a note that some brass had different extractor groove. I think maybe an old Lyman. All new brass is the same I think.

You are correct, new brass whether +P or not all extractor groove diameters are the same. I have been roloading .257 Roberts for nearly 40 yrs. and this is the first I had encountered this. Needless to say I scrapped those few pieces of brass.

It would be pretty easy to relieve the inside lip of the shell holder just enough to accommodate brass with the shallow extractor groove.

DF

I had the same issue, and it must have been common at one time. An RCBS #11 shell holder solved the problem. Found that info in an old Speer manual. All my current 257 and 7x57 brass fits in the #3.

The groove in 7mm Mauser S&B brass is larger than any other 7mm brass I've bought or been given. Privi Part. brass is standard with modern brass.

+1 If I remember right, some of the old shell holder charts gave two different numbers for the 257

I've found this too. Just don't mix brands of brass in the same run. I necked some 6mm Remington up to 257 when I couldn't find 257 Roberts brass. It takes a #11. I only use it for 75 grain Sierras so it's always separate.
I've also found instances where a Lee holder didn't work with some 7.62 Nato, but an RCBS did. Just different manufacturers dimensions stacking up.