Alexander Arms uses a 1:7.5 in their 14.5 and 16" models, and a generally a 1:9 in their 20" and longer models. There are exceptions, and a Satern cut-rifled barrel in 16" gets a 1:8 twist.
Without having done the scientific testing, it's my gut feeling that the 1:7.5 is a bit overkill in the shorter barrels, particularly if you're not going to be shooting the heavy 130 and 140 6.5mm bullets.
But, at any rate, that's how AA specs their barrels.
John
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