Bungie has said in their latest TWAB that the ammo issue will be improved for the full game. [quote]The PVE game tuning has changed pretty significantly since the Beta build was deployed. The nature of a Beta of this scale requires that it’s based off a build of the game that is now months old. So, in many cases, your feedback is helping us validate changes that were previously made based on internal feedback and playtesting. For example, we too felt that ammo (especially power ammo) was too scarce in PvE. In addition to retuning the drop rates, we built a system that guarantees power ammo drops for you and your Fireteam from certain enemies, giving power weapons a more reliable and predictable role in your arsenal.[/quote] https://www.bungie.net/en/News/Article/46077/