Since not much is open and seems too much is not very stable, I have been processing brass, lots of brass. Many brands and calibers, I seem to find cases with a "'06" base size from Remington will not go into my RCBS # 3 shellholder, has anyone else had this problem, I find they will go in a #11.

.30-06 brass case fits a Number 2 shell holder.

My Rem '06 brass fits a #2 and #3 fine. Where are you getting the interference - rim width, thickness, or extractor groove?

No. 3 is the proper shell holder, but with any caliber make or brand that can happen and seems like more these days than yesteryear, its a flaw I quality control, more common today than yesteryear also...

Just poke around and find a better fit like you did with the #11, #2 for instance or take it back to the store and get a new one or a refund, might have to contact the maker and get another, or have a friendly smith make a cut to fit..I had the same problem with a 375 Ruger shell holder recently, another a year or so ago. It happens with both brass and shell holders btw...aggravating as hell.