Well Gunslingers need Wisdom for their grit and Rangers need it for there spells so it's not a bad idea to make that one of your higher stats.
certainly wisdom is an important part of any ranger, but it doesn't need to be as cosmically high as 18 since there is only 4 spell levels and the basting is rather a secondary part of a ranger.
Gunslingers have the Grit class feature which also depends on wisdom.
Constitution is an obvious take for all classes. Everyone needs hitpoints some times.
Let's see here, for a ranger i would probably go
STR 18
DEX 18
CON 14
INT 12
WIS 16
CHA 10
Use a race with a dexterity bonus, or for Humans, Half-orcs or -elves put the bonus into dexterity. Why such a high strength for an archery ranger? Because of composite bows. They will give you a good damage modifier. Wisdom will provide you with good casting, constitution will give you a decent amount of extra hit points even if not an amazing amount. Intelligence is pretty unnecessary due to your already solid number of skill points and charisma as with most non-spontaneous-spellcaster classes is borderline useless.
As for gunslingers i would probably divide it as such:
STR 12
DEX 18
CON 18
INT 14
WIS 16
CHA 10
or
STR 12
DEX 18
CON 16
INT 14
WIS 18
CHA 10
Charisma is always the drop stat since its the least use for you. Strength at least gives you the ability to throw in a melee attack if the situation calls for it. Intelligence however is more useful as it gives you some extra skill points and helps with your gunsmithing skill. Wisdom because of grit con will make your character nice and tough and Dexterity should be your main focus recieving both racial (if you are human, half-orc or -elf) and level bonuses because it governs both firearm attack rolls and at 5th level damage.
Alternativels you could switch out WIS and CON since more grit means more gunslinging tricks, which is probably the better way to go if you want more damage dealt.
