I've been having a debate with my DM for a while now about how Composite Longbows work, and I would very much like some help figuring this out.
So, I have a Composite Longbow +2. My understanding of the bow leads me to believe that the +2 is an inherent strength rating of the bow that transfers a portion of your strength mod to damage rolls so long as you have a STR mod of at least +2. No magic involved, it just comes from how the bow is built. My DM says that that is a Masterwork level, and thus refuses to let me Masterwork my bow, and claims that I can't get enchantments higher than +2. So which of us is right? Is it a non-magical, built-in attribute of the bow, or is it a magical enchantment/masterwork?
Also, if it is the former, does that mean I can get it Masterworked and have the bonuses stack?
Edit: Oh, and if at all possible, could you include any links to relevant materials (pathfinder wiki, paizo site, etc.)?