TootsMalone

You would have an incredibly difficult time replicating the hollow chambers if your factory made jerkbaits without going the ABS route with a substantial investment into special machinery. You could make a "shell" inside your mold with some slow setting resin place your weight with bb's or whatever ballast you choose, then back-fill with something buoyant like a 2 part foam. But as mentioned above, it isn't easy. The easiest route is to make your buoyant resin baits and add ballast after curing to get the right placement and amount. My process involves having lead plugs made from various size drill bits i use for my ballast holes. 1/4" half depth, 1/4" full depth, 1/4" 1.5 depth and so on all the way up to my largest size which is 3/8" 1.5 depth. I use forstner bits for these holes so 1.5 depth means 1 and a half times the depth of the head on the bit in case that wasn't clear. You could do this same thing with tape and standard bits. Then hot glue your plugs in different positions on the bottom of the bait until you achieve your desired sink rate and balance. Just my $0.02. Good luck with your builds!

I have some experience with KBS and have done quite a bit of testing with it. Now i've never caught a Pike and probably wont anytime soon living in Florida. But we do have alligator gar and i have caught one of those. Made the switch from epoxy to KBS to avoid the fish eye issues i couldn't seem to solve. So far, my KBS baits have been far more durable than my epoxy baits. I have tried spraying it and dipping with dipping being the easiest method by far. Tried it on about a dozen baits just as it is out of the can with decent results. I did have some issues with bubbles forming on some of my more detail carved baits so i thinned the entire jar 15% with Xylene and now they dip nearly perfect. You have to keep an eye on the drips for the first 30 minutes or so before it really starts to cure. I usually re-dip after 2 to 3 hours max. If i wait any longer, then i try and put about 48 hours before i dip again to let the previous layer cure completely. It comes with pretty good instructions on re-coating. I know most of the videos i have watched people say not to let the lure touch the sides of the jar when dipping. But i dip like a mad man and bang it around in the jar quite a bit to shake off any bubbles that don't want to come out of the cracks in the scales or gills on their own. I know folks will say that is just introducing more bubbles into the liquid in the jar but i have yet to see any negatives from doing it. Maybe it is because i thin the whole quart. I feel crazy doing it and have been tempted to make a video of it just to make people cringe but it works. For me at least. Oh and i usually do between 3 and 4 coats depending on how thick they are laying down. I like my clear nice and glass-like. Hope this helps you out a bit.

Lead steel or tungsten pellets epoxied up in a ballast hole in the belly might work. Im sure others will have better ideas. I personally use a lead pot so no experience here