The value of sandbags, sleds, or even bipods at the range is found in being able to isolate out many (but not all) shooter-induced errors. Of course, the downside to their use is that it becomes less possible for shooters to blame their poor form or technique on the rifle and not on themselves as they should.

If you want to know what your rifle is capable of, shoot it properly sandbagged or from a benchrest. If you want to know what you're capable of, sight it in from said sandbagged or benchrest position and then see how well you do from prone, sitting, kneeling, and offhand positions. If the truth hurts, consider it an excuse to practice more!