barrel twist and bullet weight

[PJgunner]

Not too sure about how accuracy would be affected but stability would be the main problem.
When the AR-15* first came out for the military, it had a 1 in 14" twist as I recall. Worked just fine in warm weather but in Arctic cold bullets tumbled badly in the denser cold air. i think the change was to a 1 in 12" twist and I believe current versions use a 1 in 7" twist.

* The rifle was called the AR-15 by the Air Force and the title was later changed to the M-16 when adopted by the rest of the military.

Personally, I think going to a 1 in12" twist would be better than 1 in 14" and maybe even a 1 in 11" or 1 in 10" if one wanted to be able to use heavier bullets in or near the 70 gr. weight class. Just depends on what you want to use the rifle for.
Paul B.