Berger 20 cal 55Gr

[Hippy]

I am in the process of ordering a 20 cal bbl and now confused as to the twist. I had decided on a 9" to shoot the 50 Berger with a 20BR. The altitude here is 2800 ft . Do you belive the 9" will work with the 55 or do I need the 8"? I would also like to shoot the 39-40's and don't want them to come apart.
Thanx,
Jim