Be sure to clean all the debris and loose stuff from the barrel channel and the slots. The barrel must be fully into the stock.
Then, using the supplied tool kit, insert the drill guide in a barrel lug hole in the stock. Using the smaller of the two drillbits, insert it in the supplied holder. We recently found that it will take tools to tighten the collet enough to hold the bit solid. Insert the drillbit in the guide and with a small clamp holding the barrel tight into the stock. Just make a mark on your barrel lug. Pull it apart and look and see where the mark is on the lug. That will indicate if you have enough material on the lug to drill the hole and cut the slot slightly.