Here's how I've done it on mine. I carve the box straight through the tip then blank off the inner side with 1/8" ply which is drilled so the weight screw cuts its own thread. Then file the tapered seat and make a tapered plug. All this is done with the tip rough sanded almost to the final shape. Then tighten the plug in place and finish shaping the tip. One thing you don't want is loose bits of lead floating around inside