I have a factory rifle that shoots pretty decent, averages in the 3's but 2 or 3 in 25 shots it will drop a low flier, like 3/4 to 1" low. I have heard them called "droppers" The rifle is bedded, firing pin profiled, have shot 3 different lots of Center X, all do the same, one group will be going great and all of a sudden one will drop low, this is in a no wind situation to. Your thoughts appreciated