Sunday I tried BR2 vs GM215M.
The BR2 gave better ES, slightly better group and about 20 fps less velocity. Both with 89.1 gr of RL33 and 175 Elite Hunters.
When it is well below freezing I'll re-test.
Until then I'll continue to use GM215M , worked perfectly last season.
I do not believe you can reliably develop a load for one primer and then just pop in another primer and get best results. If you what maximum accuracy for each primer you need to develop a specific load for each and most of these magnums we shoot have such short barrel life I am not willing to do that. Sure sometimes people get lucky and substitute one primer for another and have excellent results but I would say it is the exception not the rule. Pick your primer and stick with it. My second choice would be a 250 but I have never had a problem getting single digits SDs with 215Ms so I will stick with them until they won't work.
I have loaded for 9 different 28 Noslers now. Starting #10 next month. In every single one I have used CCI BR2. With phenominal results in both speeds, ES/SD, and accuracy. RL33, between 3080-3150fps using 195 Berger EOLs. From sub-freezing to 110°. Whoever says they are not enough for the 28 Nosler is incorrect. Ask Ryan Pierce (Piercision) and Eric Goss (Axisworks) what they recommend.
Federal 215 and CCI 250
Both have given excellent results, in two different rifles
Retumbo and H-1000 are the powders that I have been using. Have just recently used Bertram brass (CCI 250's) in a new GAP built 28 Nosler and it appears to initially be better than Nosler brass.
I would of never thought people would be using BR2 primers for RL33 or any slow burning dense powder. I would be curious how they hold up in cold weather. I do test primers once i have reached a point during load development that i am happy with. In my 28 Nosler with N570 Fed 215 worked best. 338 Edge and 7 Saum along with 30/28 Nosler all like CCI 250 better. Pretty easy to test. Last time i talked to Ryan Pierce he was using CCI 250's...