Spoopa,
Thanks for the words of encouragement.
I'll keep the faith.
Pete,
I also found out that I needed to have the lure's nose pointed, like you did.
I make my four piece lures with weight near the hook hangers in the first and third sections, and that seems to make them swim well, and turn 180 degrees on a pull/pause. I typically weight them until they float level, with temporary weights on the hook tines, and then add the additional weight using 1/4" lead wire, which weighs 1 gram per 1/8". I cut it with a drywall knife, rolling it back and forth like a tubing cutter, roll it on my tablesaw top with a piece of 1/4" steel to get rid of the raised edges, and then push it into a 1/4"+ hole. A drop of crazy glue holds it fine. Then I bondo over the top to hide the hole.
If I want a sinker, I add the additional weight both toward the nose, and in front of the rear/third section hook hanger.
I don't think the grooved head is the problem. I started doing that with some three piece lures I made, and they swim fine, with the head stable, and the tail flapping like a flag in the breeze. But all my lures are taller and thinner than yours seem to be. My 4" bluegill, whose body is only 2 3/4" long, is 1 1/4" tall, and only 5/8" thick at the mid point. My 6" three piece bluegill/crappie lures, with 4 1/4" bodies, are 2 1/4" tall and 3/4" thick at the mid point. They all taper back from a more pointy nose to thick and the first joint, and then back down to thinner (3/8") at the tail.
I also taper them top to bottom, so they have a V profile, like a battleship. I think this keeps them stable at high speeds, so they don't roll on their sides.
atrophius,
I actually do that kind of bulb on the end of the tail section on my four piece lures that have a spring holder for a plastic tail. I did it to give me enough space for the tail to mount, but not have a really thick lure most of the way back. It kind of flares out at the tail. They swim fine, so I guess it works.
Tim,
I copied your double split ring tail on the one I just made, to try and keep the size down.
Man, what a pain to get split rings through the plastic without springing them open!
I wound up using #6 split rings.
If it swims better, I'll probably find some better, smaller rings. Those big rings are gaudy.
How big are your bluegills?