Hogger,
Not that I have any objection, each to his own, and viva la differance. But, in this case (pun intended), I just hafta' ask: WHY??? What's wrong with the .243 Win?

My wife shoots one of these. Excellent cartridge. For her, it is just that bit more pleasant than the 243, with little loss in performance.

We didn't have a dedicated reamer, but used a 22/250 reamer to cut most of the chamber, and a separate reamer for the neck. So, the round we ended up with is a pure 22/250 necked up to 6mm. The shoulder retains its angle and position.

Barrel is a 1:10 twist, and it shoots 65 and 70 grain bullets very well. Haven't tried anything heavier....we use the 243 for that.

For dies, we are using a Redding 6/250 competition seater. To size the neck, a 22/250 bushing die, with a bush around the .260 level works just fine. I haven't had to push the shoulders back at all, but a 22/250 body die will work.