As L.Sherm mentioned, getting 4100 w/40's from a 20BR will be a bit of a stretch unless you run it really hard at some pretty high pressures. If you want to drive a 40 grainer that fast, you'll be better off stepping up to the 20-250 which is another very easy 20 Cal to make.
I've got a couple 20's, 20-222 w/11 twist that shoots the 40gr Bergers, and a 20-250 w/8 twist that shoots the 55gr Bergers. Both are a lot of fun and very accurate, but they definitely have their trade offs.
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