A slot is a long, or elongated hole in the barrel hanger, to allow movement back and forth along the length of the barrel of the pins, or keys, that hold the stock to the barrel. This allows movement due to swelling of the wood in wet conditions, and shrinkage during dry winter months. If the slot is not there, the pins or keys will bind, cause the barrel to move from shot to shot as the barrel heats up, and then cools down. Sometimes the wood will actually warp permanently, and that will certainly cause a change in POI, with subsequent shots going who-knows-where in a match, or during load development. The slot needs to be elongated so that its at least 3 widths of the pin that holds the stock to the barrel. Some can get away with less, but why take a chance. The pin is held in its " center" by the holes in the wood of the stock, and any escutcheon that might be used around the pin holes, and will not move. Only the barrel will seem to move back and forth, when in reality it is the wood that actually moves, while the pins and barrel remain stationary. Its the swelling and shrinking of the wood that makes the pins appear to move back and forth in the slot.
