I interchange them quiet often in the 6mmBR Norma. Some powders work great with the CCI BR4's and/or Rem 7 1/2's. My most consistent and accurate loads seem to come from using CCI-450 SRM's.
I saw a mention above of the Rem 6 1/2's. I read some controversy about them from a few years back. Someone was saying they were developed by Remington for low pressure cartridges, like the 22 Hornet, I think. It also went on to mention that they should not be used in .223 loads but I think they were meaning to say AR-15 loads, as the cups are thin and susceptible to slam fires in these semi's.
I have and can confirm that they behave and shoot just fine in bolt action .223 Rem's. As a matter of fact,
6 1/2's with 25.4gn of Viht N133 and 50gn VMax's is very accurate to 600yds in my Marlin X7VH.