This is directly from the Remington website:
"In pistol cartridges, the 1 1/2 small pistol primer should not be used in the 357 Magnum, 357 SIG or the 40 S&W. The 5 1/2 small pistol primer is the proper selection for these rounds.
In rifle cartridges, the 6 1/2 small rifle primer should not be used in the 17 Remington, 222 Remington or the 223 Remington. The 7 1/2 BR is the proper small rifle primer for these rounds.
Warning: When primers are selected incorrectly, misfires, damage to your firearm, and/or personal injury may occur. Visit the ballistics tables on our website. Recommended primers for each rifle and pistol cartridge are listed in these tables."
http://remington.custhelp.com/app/answers/detail/a_id/167
Ain't this a crock?? I am told that some of the boxes of 6 1/2 have a warning on them while other boxes do not!! I did a little research into this about a month ago and found the following interesting ... Here is a response from Remington when presented with the question about using 6 1/2 in the .223 (bolt type gun)
"Thank you for your question. Some handloading books call for the 6 1/2 Primer we recommend the 7 1/2 for the .223. Both primers are correct. Both primers are the same size but the primer cup on 7 1/2 is made of thicker metal. Remington feels with the higher pressure on the .223 it would be better to use the 7 1/2. I hope this information was helpful. Thank you for contacting Remington!"
Some data about primer cup thickness:
Rem 6 1/2 - .020"
Rem 7 1/2 - .025"
CCI 400 - .020"
CCI 450 - .025"
CCI BR4 - .025"
Fed 200 - .019"
Fed 205M -.0225"
Win SR - .021"
Using this info and Remington's logic, it would seem that the CCI 400 would be in the same boat as the Rem 6 1/2 ???
After all my research, my conclusion is: Use Rem 7 1/2, CCI 450, or CCI #41 in AR type rifles chambered for .223. I have used a couple K of CCI 400 without mishap or problem. However, also used Fed 200 and had a slamfire in a Bushmaster - I blamed it on not seating the primer correctly - now I am not sure!
Another thing - from experience - do not use Federal small pistol in a .223 AR .....