After laying out the 4 bbl lug holes and/or the 3 RR pipe holes, the drillpress setup is shown w/ the bbl/stock ass'y clamped in a very square vise and the top bbl flat is against the permanent vise jaw . A parallel is used somewhere under the muzzle end to maintain the stock/bbl ass'y's horizontal position.
2 parallel clamps are used to ensure the stock/bbl ass'y is held tightly together and are on both sides of either the bbl lug or RR pipe and after the hole is drilled through, the pin is pressed in and the clamps are moved to the next location.
All the pins in my builds are lengths of 1/16 dia. music wire and a 1/16 drill is used . Once the ass'y is positioned w/ the center punch under the 1/16 drill, the hole is drilled through to the other side w/ many chip clearing withdrawals.
Drilling the 4 bbl lug holes takes approx 15 mins and the 3 RR holes a little less. Never timed the hole layouts {goes pretty fast} but the vertical dim mark is done w/ a depth mike ....the webs are only 1/16" at the breech and 5/32" at the muzzle so some accuracy is req'd.
This same setup is used for drilling the front and rear lugs of the TG and the pivot pin for the trigger. Also the ass'y has to be repositioned end to end for the bbl lug and RR pipe at the muzzle.....no big deal.
Have tried other ways to drill these holes but prefer doing it as described because of the excellent accuracy and speedy time......Fred