Not 1:9 preferred. If you want to stabilize the 20cal 55's you must use a 1:9. I have a couple 1:10 failures on the shelf because they wouldn't work for the 55's. One is an Excalibur 20BR and the other is a Benchmark in 20-250. They both shoot well with 50's and shotgun the 55's.
Good to know - thanks for the input!
I have read a few threads on it and 1:9 seemed to be a good consensus. Seemed like the 8 was fine for 55s also but too fast for 39/40.