side note but related does 1-7 have a negative effect on lighter bullets ??
i believe that a 11-7 twist barrel can over stabolize a lighter bullet causing to the lighter bullets nose to dip down at longer ranges. i not 100% sure on that it just seams i read it somwhere
You're on the right track. Over-stabilized bullets will fall back to earth with the point/tip still pointing up (same orientation it had when it left the bore).
Not really germane to the conversation at hand, so carry on.
To the OP, I didn't see someone specifically answer the question, so I'll explain it, in case you were looking for a very basic answer. The 1 in 7 (or 9 or 12 or....) means that the bullet will perform one revolution in the number of inches specified by the larger number. So, a 1 in 9 twist barrel makes the bullet spin one complete revolution every 9 inches of travel. A 1 in 7 spins the bullet once every 7 inches. Therefore you can see that the smaller the number, the "tighter" or faster the twist of the rifling will be.
Urban legend has it that the 1/7 will spin a light bullet to fast and it will explode, Ive never seen it happen. I belive stoner set up the first AR's with a 1/14 twist .A 1/7 twist has one turn of the rifling in 7 ", a 1/14 is one twist in 14", so that would make the 1/7 twice as fast as a1/14 TTBOMK