I think what your saying is that the round being pushed forward by the bolt pushes the belt of the round below and the result is a feeding jam. The 30-338 is a very 'square' round. that is there is little body taper. It fosters this kind of problem. A magazine mounted guide to force rounds to move to the rear as they are forced into the magazine is whats needed. This is not an unusual problem. Rimmed and semi rimmed rounds can all create the same situation. Angled metal strips in the mag well such that they fit in front of the belt but stop below the top round in the magazine will solve the problem. They force the round below to the rear as another is loaded into the mag. This relationship is enforced by the rib and if the belt can't get behind the belt of the round below, it can't grab it. The angle does not have to be great. Just enough to keep the lower rounds just a bit back of the round above. You may also have to widen the magazine box for the larger case diameter.