I had the same thing going on, I could go to the range and shoot under half MOA at 100 yards and when I get to the match my groups would open up terribly.

What I have found that it is all boiling down to is my load. The load that I chose is awesome for up to 7 or 8 shots, then when the barrel and chamber get hot things really go south.

At my last match a guy told me " you might have a good hunting load, but you need to develop a load for a hot barrel. Try backing off the powder charge 1/10Th grain at a time until it's back in the sweet spot." I thought wow, I never thought of that but it makes a lot of sense.

Take a look at my first comp targets in this under first 200 yard F Class results by DanSavage