Next layout the holes for the clamping screw and if desired a sling swivel mount. If there will be no swivel attachment on the barrel band then center the clamping screw under the magazine tube for a nice symmetric look, this style looks good if you make a clean arc shape under the clamp screw for final shape. Make sure the hole is far enough away from the magazine so the threads will not cut through the wall of the magazine tube hole. A 10-32 clamping screw works well and will hold up for many years of use and abuse. For the screw hole I drill to tap drill size and countersink for the head of the screw so it will be flush when assembled, nothing to snag on. Drill them all the way through but that is for simplicity, you could make blind holes for the clamp screw if you think that would look better. To save unnecessary work measure your sling swivel to make sure it will clear the side of the barrel band (see picture).
At this point is when I trimmed my oversized block to the correct length.Looking at the pictures accompanying this article you will note that I undercut the clamp area of the band a little narrower to make the band look less blocky. This also helps to get the swivel mount closer to the center line of the gun. Undercut these areas between .075” and .100” depending on your desired finished dimensions. Using a ball endmill will provide a nice contour at the transition points. I also use the ball endmill to rough out the grooves on the side of the band between the barrel hole and the magazine hole. Now if your doing the sling swivel mount you can cut away the unneeded material, opposite the swivel mount, see photos.
My bands generally end up about .075” thick over the barrel, they can be made thinner but as long as they look good I figure the added weight is a good thing. I layout the center-lines for the barrel hole first keeping wall thickness in mind. Then simply take the radius of the barrel and magazine holes add them and add the measurement you took with the feeler gauges for the gap between the barrel and magazine. That gives you the location for the center of the Magazine hole in relation to the barrel hole.
I then set up in the mill and rough out both holes, keeping track of my zero so I can move back and forth for the finish boring of the holes. Final sizing of the holes is accomplished using a boring head in the mill. If you don’t have a mill you could do this work on the lathe using a four jaw, it would just take more set up time. Once the holes are bored to the desired dimensions I test fit them to the barrel and tube. Ideally the barrel hole should allow the barrel to slide close to the finial position so that I can adjust it with a rawhide mallet for position and alignment. The magazine hole should be close slip fit.
A slitting saw is used to make a slot from the bottom of the barrel band up into the magazine hole. This could be done with a hacksaw or bandsaw, but I like the finished look of the slot using the slitting saw. If your going to include a swivel mount be sure to consider that when choosing the location for the slot. Once the slot is cut be sure to go back to your clamping screw hole and drill a relief so that your clamping screw will actually clamp the magazine tube. This is the time to drill the relief because you can feel when you hit the slot, no measuring for depth needed. I actually use the relieved hole as a tap guide and tap the hole for the clamp screw at this point.
Note that the corners at the bottom of the barrel band were radiused to allow the swivel to swing, and for a more finished look. The picture at the left also gives you a clear view of the gap between the barrel and the magazine tube.