J E-
Thanks for your reply to this post as well as my June 4th post (Switch Barrel .22s)
Other people might not have a lot to say, as my shooting interests are sorta out in left field!
If you scroll down this page, you will see where others have had custom 1:9" barrels made for the 60-gr Aguila rounds.
I have heard from Redmann Reboring to say that he can probably reline a Marlin Papoose barrel with either 1:9 or 1:24. (He needed to see the bbl) The latter would be good for .22LR CB Caps, which are quiet. I never could get the CB Caps to group well from the std .22 LR barrel, which, as you say, is most likely around 1:15. I do not think it is the rate of twist so much as the way the CB Cap lies too far behind the leade of a regular .22 LR chambered bbl. The std .22 LR (40 gr) should sit well in the leade of a rifle chambered specifically for the 60 gr Aguilas.
I think RUGER should offer 12" bull barrels for their Charger pistol. Perhaps in different twists,