In my experience, a gun will show preferences for certain loads early on. Many barrel makers say that their barrels won't shoot to their full potential until they have about 100 rounds through them. Many Shilen barrels I have installed were that way. A load that shot about 1" in rounds 11 through 15 might shoot close to 1/2" at rounds 101 through 105. And a load that shot 3" in the early stages of break in might never shoot better than 2".

Having said that, my Jeff Lawrence 6MM-284 barrel shot the first 5 bullets I put through into 1/4". Didn't improve much after break in.