Well here's some measurements. Water capacity of both calibers is within .7 grains. The 243 holds 55.5 gr. of water, the .223 holds 54.8.
overall length of 8 fired cases, half .223 the other half .243 is average of 1.667 rim .535 for bolt
Base just ahead of the extractor grove .551
expansion ring- .557
length to beginning of shoulder 1.130
length to beginning of neck, 243 1.409
length to beginning of neck, 223 1.422
O.D. of neck, .243 .285
O.D. of neck, .223 .274
This is a rebated rim the same as the WSM family. It is the same rim size as all belted magnums. The expansion ring,(just forward of the base measurement) was quite noticeable, but not excessive.
I probably took 20 shooters out to try these rifles. Most wanted to try the .223. The Browning reps said to try and steer them to the .223, they had more ammo for it.
Saturday I worked with the guys from Ruger. They brought the 480 super redhawk, 9.5 inch for people to try. With 325 gr. xtp mag bullets at 1320 fps, it is quite a handfull. I got to shoot it late in the afternoon. Wow, that's the most recoil I've ever felt from a magnum handgun! It's quite accurate though, I hit the rubber target 4 out of 5 trys.