jepp, I suppose I could have measured the cases that need modification but I didn't. I used the country boy approach and just set back the shoulder enough to chamber. And maybe you didn't read the whole thread, but the loaded rounds were for a previous 260, and that rifle had a more 'generous' chamber. For the new rifle I started with the body die screwed down to where I could feel the shoulder of a round loaded for the new rifle (with a fireformed case). Then, in small increments, I turned the die in on empty cases until I got them to chamber. Took quite a few small incremental turns to get there.
The long term plan was to begin using the Lee Collet Die once I needed to reload again and then use the body die when rounds became difficult to chamber. The flaw in the plan is that I wasn't expecting the rifle to shoot that darn well, but now that I see how well it shoots with ammo loaded with standard dies, I probably don't need the Lee die. And I possibly may never need the body die again. But if I do...