help with rate of twist in M77V .280

[Talltexanrancher]

I have a 25 year old Ruger M77 Varmint in .280 with the heavy bull in 24".  I'm trying to find its rate of twist.  It seems to like 130's and below, and dislikes anything above that.  I would appreciate any help you could throw my way.

[bull b 25-06]

hey here hope you find this. It sounds so simple but it works take a cleaning rod and put a patch on it like you were going to clean the barrel. Then take a black markerand make a markon the rod as a starting point,and make other marks such as 7,8,9,10,12 inches from your first mark.Then make a mark in line with the rod toward the end of your last inch mark. Then simply insert the rod into the muzzle and at the starting mark turn rod so the inline mark is visible. Push rod until the inline mark comes back around and there you have it. later bull b 25-06