I was just loading some some 6.5x55 useing the #3 shellholder and happen to look at the RCBS die box and it said shellholder #2.
Yep, 6.5x55 brass, chambers and reloading can be an adventure, for sure.
The main rule: There isn't a rule...
What you see is what your get...
A great round that can get a bit quirky with various makers of brass.
I'll again plug Lapua brass, especially for this round. Once my Mauser was set up for this brass, I've never looked back. With Lapua, you know what you're getting, no surprises.
DF