Mine actually does have a 1:7 twist. Says so right on the barrel. I think you can go up to 82 grain bullets in a 1:7. See www.bergerbullets.com/pdf/Quick-Reference-Sheets.pdf. 80 through 82 grains max, although I never have. I think 77 grains is as heavy as I have in the shed., I shoot 55 grain bullets through mine all the time and they do fine at 100 y (short range to many of you. But that's what I've got.) That Berger chart suggests you need 1:6 to stabilize a 90 grain .223 pill. Dunno from personal experience, as I said above.

Here's a target that I am not particularly proud of, which shows different bullet weights at 100 Y off of a bench/BullsBag out of the Savage 12 F/TR in .223 (1:7). This from when the barrel was brand new and I was testing different factory ammunition in the rifle to get a baseline for performance at 100 yards.