It defo would increase accuracy. Madbull BBs are pretty much the best BBs I have personally used, although ICS, ASG Blaster and King Arms make very good quality too. I only use .2 to chrono my gun after teching, n .25 or .28 for skirmishes.
Note: It will not just improve accuracy, but range too due to better flight against wind resistanve and it'll maintain its velocity much better.