Is there a place to get a definitive answer as to what twist rate a particular rifle has? I have a Ruger M77 MK II chambered in 260 Rem. The gun was purchased new by my father in Dec of 2003. I emailed Ruger a while back, they said 1:8.5. Then later I saw another list that said 1:8. I am just curious as to which it really is. I am thinking it may be the 1:8, because I shot the 140 Accubonds out of that rifle with sub-moa accuracy.
I tried the measuring thing in another rifle, didn't go so well for me as I tend to be all thumbs with that sort of thing!

try the Tube

Just push a tight fitting patch down the bore with a piece of tape wrapped around the cleaning rod to make a flag or tab near the handle pointing straight up. Mark the rod after you have pushed the patch into the rifling at the front of the chamber. Push the rod down the bore and watch the flag rotate one complete revolution until it points straight up again. Measure the length from starting point to finish on the rod and that is the twist rate.

Good video, short and to the point.