I appreciate the suggestion. I absolutely could do that, and may end up doing so, but I’m a little concerned the small drill will wander in the soldered-on block, since it needs to drill through the outside block, the solder, and the barrel lug itself, all of differing hardnesses. Also, the hole will be right on the block/lug seam. I feel more comfortable drilling the large detent hole to depth with a rigid center drill, then coming in from the forcing cone end with a long, small diameter drill, or even from the muzzle end using a standard length bit.
TBR