The 6 CM would have as big a boiler room as you'd probably want to go unless you really don't care about barrel life. I'm guessing they're good for 800-1000 full-noise rounds. They're bigger than a 6x47L so have to be worse if you're running them fully.
There's no way past the trade-off between wind drift and barrel life. That .243 BR-K is only 20% better than a BR so you'd have to go right up to a 6-284 to make great inroads into wind drift. If 600 rounds per barrel doesn't scare you, fill ya boots
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