[RPG] Adding adaptive to composite bow

It does not auto-adjust.

I agree with John Campbell of the giantitp boards on this one. When the Bone Bow says that it

functions as a composite longbow with regard to applying the user’s Strength bonus to damage done with arrows shot from it. (75)

I see no reason to assume that it only applies to parts of the rules text concerning composite (long)bows and their interactions with the wielders Str bonus.

All composite bows are made with a particular strength rating (that is, each requires a minimum Strength modifier to use with proficiency). If your Strength bonus is less than the strength rating of the composite bow, you can't effectively use it, so you take a -2 penalty on attacks with it. The default composite longbow requires a Strength modifier of +0 or higher to use with proficiency. A composite longbow can be made with a high strength rating to take advantage of an above-average Strength score; this feature allows you to add your Strength bonus to damage, up to the maximum bonus indicated for the bow. Each point of Strength bonus granted by the bow adds 100 gp to its cost.

The only clarity issue here is the pricing of the modifier, which differs between the Longbow and the Shortbow

Each point of Strength bonus granted by the bow adds 75 gp to its cost.

Considering that 100 and 75 gp are the base costs for the composite long- and shortbow respectively, it can be assumed that every point of Str modifier costs the full base price for the bone bow as well, which makes the bone bow quite expensive, especially considering the feat requirement.

Should it?

On the one hand, I'd say it shouldn't, because I can't really justify it in character/in world, and my gut says no.

On the other hand, both (most) archers and exotic weapons are well known to be rather weak in D&D 3.5, even compared to other mortals martials. Giving them a boost (which mileage varies widely depending on how often you Str rating changes) is certainly not game-breaking, especially if they need to burn a feat to use it, on top of those other restrictions.

The Giant Hunter's Handbook (Jan. 2015) includes the magic weapon special ability resizing (4,000 gp; 0 lbs.) that says

A resizing weapon instantly shrinks or grows to suit the size of any creature that picks it up unless it is currently wielded by another creature. It reverts to its original size 1 round after it leaves its wielder’s possession.

From what I can gather, the weapon special ability isn't limited to melee weapons. As a relatively new release, the Handbook's information is likely still being readied for inclusion on d20PFSRD.