I have been tempted to use the BR2's in the past as they are quite a hot primer but personally i would not use a standard run of the mill large rifle primer, its a large column of powder to get a nice clean even burn and standard primers may not consistantly provide the spark thats needed. As for the groups opening up, with the Federal Gold Medal Match Magums my custom rifle shot so well i dont think a different primer could improve it, i have shot 2.5" groups at times at 600 yards so for me with manual human error involved i was more than happy with that. I am just concerned about having changed to Federal Champion Magnum primers it could have changed my loads performance from the load i developed? I will report back when i have had one evening this week to shoot some of the loaded rounds i have made using these primers.