If you cant get the CCI 450s then the CCI BR4s also have the thicker cups. I use both primers and have found them interchangeable with bugger all velocity difference between them.
What ian says appears to be true, they interchange in my 308 fine. Only real difference is one has a small "b" on the cup and you pay more for it. Using between 45 and 46gr of 2208.
Heres one on small primers. It doesnt show the CCI450, but I believe its not all that different to the flash of a BR4, with a slightly hotter flame. Rem 7.5's didnt perform well for me in the 308 but I used the last of the ones I had for fireforming ammo in my 260 improved and they shot quite well. I wont be buying anymore though as I found a batch of 450's that work well in all my loaded ammo so I stocked up on them just a little. (Shouldnt run out of primers for the next couple of years)