When thinking of a barrel twist for a 25, it might pay to think of it as a 6.5 since the .007" difference isn't really all that significant. In 25 caliber, the 120 is percieved as being a long, heavy bullet. In a 6.5, it's a lightweight. Perception.
This is evn more apparent when you measure the length of the bullets. A 120 grain Speer spitzer in 25 cal is 1.075" long. The same weight bullet from the same maker in 6.5 mm is 1.070. By way of comparison, the 140 graim 6.5 is 1.2 inches long.
Now, a nine twist will stabilize a 6.5 140 just fine. A twelve inch twist will stabilize the 120. Reduce the diameter to .257, and things don't change much. I don't have a Berger 115 to measure so I can't comment on it. I also don't have a Barnes 120. These bullets may be long enough that the standard ten inch twist won't handle them but I can't say for sure.
I do know that for myself, I would use a ten, for a customer, I would do what I was asked to do! GD
