Really its not a "gun issue"... both Sodak and Norcal guns have bad spread, the main difference its angle and the little range advantage on Norcal ones... BTW... you should use norcal guns above norcal... its foolish to waste the extra range and AP
but the main thing it's that you can drive with lvl 65 support crew a Colorado and it WILL work fine enough, but if you try to go battle with a lvl 73 crew on a US BB3 you will get screwed...
to use decently your BB3 you should get your Engys and Reps up to lvl 78 or 80, up to that point keep on Colorado, you will have better results.
With gunners its about the same... the general rule that your gunners should be at least 10 lvl more than the guns ure' using with BB3 i will say that this extend to 15 lvls... with less than Lvl 90 gunners you can't really have a decent spread.
Once you get the supports and gunners to the right lvl you will be doing some decent damage per battle