Bear 24 is right on. The #2 position is the Average position. Without looking at the Ruger material I don't know what their "average" bullet Wt. etc. is, however; on many adjustable gas systems, the drill goes something like this, turn down, won't cycle, move up until it barely cycles (some short strokes, stove pipes etc), move up one from there, and drive on! This way you're getting all the gas you need, but not a lot more.
According to the Ruger On Line Owners Manual:
There are three other gas port settings labeled “1,” “2” and “3” which vary in size, with “1” the smallest and “3” the largest. (See Figs. 30 - 32 on page 35.) Use the smallest gas port setting that reliably cycles the action with the particular ammunition you are using. There is no benefit to running the rifle on a gas port setting larger than is necessary, and doing so may degrade long term endurance. Most commercial ammunition will cycle optimally on setting “2,” which is an ideal starting point when first shooting the rifle with new ammunition.
Figure 28
Figure 29