I selected an old crankbait that I almost never use. This is a Matzuo crankbait which dives to about 8-10 feet. When I get this procedure down and tested, I'm going to have a rattle and a silent version of the same crank bait so I could switch back and forth. Silent cranks are often effective on highly pressured fish. Lots of pro anglers switch between rattle and quiet cranks when the other stops working.
1) I took the treble hooks off the crankbait and located where the chamber is by shaking the lure and feeling where the most vibration is occurring. In this case, it seemed to come a little less than half way between the front and trailer hook eyes. Mark the drill point with a Sharpie.
2) I put the lure in a small vise. I put a block of wood in the bottom of the vise to keep the lure body from falling through. The vise is actually clamping down on the wood block rather than the lure body. The lure body is actually held in place by the wood wedges that I had handy. I just slid these wedges on either side until it held the lure firmly with no play.
2) I selected a 7/64" drill bit. I took the drill bit and put a dimple where I wanted to drill. I did this by pressing the drill bit into the spot I wanted to drill and then turning the bit with my other hand. Since in this case the plastic underneath the paint appears to be clear. I chucked the drill bit in a hand drill and drilled the hole.
3) I took the lure body out of the vise to see if I could see the BB's. The BB's could be seen if held a certain way. Then I re-secured the lure body in the vise.
4) The pros say they used heated silicone on their silenced lures. So I used standard kitchen and bathroom silicone and warmed it up in a hot water bath. The reason for heating the silicone is to soften it so it would flow more easily. I used hot water from the tap, which is about 110 degF. If I were to do it again, I would put the water on a stove and heat the water to about 150 degF. The silicone did seem to flow easier, but I think if it were heated more it would flow a lot better.5) I then squeezed a small amount of silicone (about the size of a pea) into the hole and worked it in with a tooth pick. I took the lure out of the vise and shook it to disperse the silicone and get the BBs coated. I heard the rattling decrease to a mere muffle.
6) I then whacked the lure against the workbench to seat the BBs on the bottom of the rattle chamber. I gently shook the lure and it was silent.
7) I filled the hole up with some more silicone and set the lure back on the vise right side up, to keep the BBs on the bottom of the rattle chamber, and let the silicone set overnight. I used silicone instead of epoxy because it was handy, its supposed to be waterproof, it matches the lures underbelly, and I was too lazy to mix up some epoxy.
UPDATE: The hole really has to be filled with epoxy, or something durable. The hooks from other lures poked a hole right through the silicone. To minimize the mess of smearing epoxy all over your bait, I would advise to tape the lure before drilling the hole. This way, the silicone and epoxy will stick where it needs to and not stick to the outside of the bait. After the epoxy has firmed up some, remove the tape. The thickness of the tape may also help with the epoxy "shrinking" into the hole. I got a divit in the epoxy and I think this was caused either by the air cooling off inside the rattle chamber after I had handled the crankbait, or the walls of the bait relaxing after being pinched. The epoxy sagged into the hole. I followed up by putting on gap filling cyanoacrylate.
