BR primers are said to have thicker cup material and are safe to us in AR type gun with out fear of Slam fires. I have not measured the thickness, but it seem to be the consensus. I am using CCI BR in my AR right now because that is all I could find at the time. Seems primers are getting more plentiful. Powder Valley has CCI # 41 in stock just a few minutes ago, web site may not be up to date
Jimmy K
Do a google search on primer cup thickness, you'll find several pieces about primer cup thickness. Of the measurements that were tested the BR came up thicker by .002. Like I said I did not do the test, only read about them. Add a half cup of salt and ....