I just picked up a new upper at the KC gun show yesterday. It has a 24" black rain mediem contour barrel 1-8 twist .223, free float, dpms slick side reciever. I shot a few different loads through it yesterday and found it to shoot 40gr sierra varminters the best. My problem is that it walks down as it warms up, by that I mean after the first shot. If I fire two shots within 30 seconds, the 2nd shot will hit 2" low. If I fire a third, that one will hit lower still. After a few minutes of sitting, the poi will go back up. Shot group if I take my time is 3/8 wide, 1 1/2 tall. Anybody ever seen a barrel walk after one shot?