JG Bar-10 Accuracy Probs

First off, I am new to sniping. I recently bought a JG Bar-10 rifle. I like everything about it, except for the accuracy. I measured my shooting distances, and the rifle is perfectly accurate at 105 feet. However, at 150 feet, the rifle is very inconsistent. The scope has been dialed (at least, the best it can), but it is still shooting pretty bad. On occasion, I will have a shot spin off to the left or the right, hitting up to 10 feet away from the target. I've read that with this gun, I should be able to hit a head sized target from 150 feet. That is not the case. I am using .25 High Impact Crosman BBs. Is it possible it is the BBs? I doubt that, as they are seamless and appear perfect in shape. Any help would be greatly appreciated.