Since I started building MLers, drilling the bbl lug and RR pipe holes always took too long ....anyways to me. So, bought a "C" clamp type drill jig and was disappointed that it was very slow also. Experienced builders aren't my concern because they probably have their own way of doing this, but possibly many beginning and intermediate skilled builders might be interested.
I first lay out the horizontal hole locations w/ a depth mike laying it on the top of the forestock and just eyeball for the vertical lines. A sharp awl is used to carefully indent the intersecting lines.
I do this drilling in a drill press that has a reinforced 3/4" thick X 2'X4-1/2' sheet of plywood bolted to the DP table....it's never removed.
The bbl/stock ass'y is clamped close to the breech in my super accurate vise w/ the bbl top flat against the permanent jaw of the vise. A parallel is towards the muzzle which keeps the ass'y horizontal.
A parallel clamp is on each side of the bbl lug , the awl indent is picked up by the 1/16 drill w/ an RPM of 1300-1500, centered on the indent and the hole is drilled through. A length of music wire is inserted into the hole , the clamps are moved to the next hole and everything is repeated until the 4 holes are drilled.
A 3/8 dia steel dowel is inserted into the RR pipe and one parallel clamp on the top of the RR pipe holds the pipe and ass'y together. The hole is drilled through and a length o 1/16 dia of music wire is inserted and the clamp is moved to the next RR pipe and everything is repeated until all the holes are drilled. The dowel must be shorter than the pipe so it doesn't bear on the RR groove.
The 4 bbl lug holes take 15 mins to drill and the RR pipes slightly less.
To drill the holes for pipe or lug at the muzzle, the setup must be changed end for end which isn't a big deal....takes a minute at the most.
The webs at the breech are 1/16" or slightly less and require very accurate hole locations and drilling. The bbl lug at the breech is shown as well as the vise I use and the drill press setup. Have been doing this for 35 yrs or more and it has always worked.....Fred