Wow, I just noticed that about Double-Musket
One would pray it's somehow a misprint, not even the Double Barreled pistol is that bad! And in fact, the Double Pistol has the SAME range as the basic Pistol.
I CALL SHENANIGANS!
On a side not, the Reliable enchantments can negate the drawback, and the reason I like Double barreled
Pistols is that you can "swift-action" reload them with weapon cords (see the Reload mini-guide for details).
As for the Musket problem... you could always take 3 levels of
Luring Cavalier, it lets you target Touch AC up to 2 range increments away, add in the Distance enchantment, and you're (sadly) back up to 40ft.