I just shot my brand new .243 last weekend. I shot 5 times, cleaned it with #9, shot 5 more and cleaned it again. Then i finished off the box and cleaned it again. I do not think there is any real benefit to "breaking in", but most factory barrels are not high quality anyway like a hart etc. Too much time to clean after every shot, not sure what that actually accomplishes anyhow. I have read that breaking in a barrel simply means you are coating the fine spiral milling grooves in the throat with copper, which smooths them out since they are perpendicular to the barrel grooves. That is why moly is not a good choice for barrel break in.
