You might find this project that my man has been working on for the last few months interesting. He actually got several samples from the guy who is machining the die for him to test a couple weeks ago and posted a test reveiw sort of like you do (nice web site by the way), his test results pictures are on the second page I think:http://castboolits.gunloads.com/showthread.php?t=41865
The 410 is a little dinky gun in my opinion when it comes to a longgun full size shotgun, why not just use a 12 or better yet a 10. I do like those little 12" long double barrel side by side pistols that take both 410 and 45-Colt and 454-Casull. I've got a brace of them I use in cowboy action shoothing. I imagine the ballistics from their longer barrels is better then the revolver gun you reviewed. My hand load of choice is three 395 balls cast from WW from a Lee ball mold with the powder charge for a 3 inch shot load underneath them with a stack of nitro cards inbetween ball and powder.
The fins in the very first picture of the thread you linked to above were machined by myself for turbo1889. I am hoping he gets that project up and going so I can give them a try.
As for the 410 slug I came to it in a very long route. I wanted to hunt deer with a lever action, but I live in a shotgun only state so 99.9% of all lever guns were out (the Winchester 1887 and 1901 being my only options that I knew of at the time).
So when Winchester introduced the Win 9410 I got real interested and ended up buying one. It looks and feels just like a Win 94 in 30-30 and even has a side loading gate (a big draw for me) but chambered in the 2.5 inch 410 shotshell. When I bought it I really didn't think I was going to hunt deer with it, at least not to seriously, but I thought I would at least play with slugs and see what they would do. I was mainly going to use my 9410 for squirrel and rabbit.
I was at the range shortly after getting the 9410, there primarily to sight in my muzzle loader, but I had bought some slugs for the 9410 and figured I would give them a try just so I could say I gave it a try. One of my first groups I shot with the 9410 was a five shot, 2-inch group, at 50 yards with 410 Remington Sluggers. I was stunned that a smooth bore shotgun could shoot slugs that well, and on top of that I didn't have a bloody-nose like I so often got from 3-inch Remington sluggers out of my 12 gauge BPS.
So I started doing some research and testing. I convinced myself that if I kept my shots close the 410 slug could take a deer. The first day I hunted with my Winchester 9410 I took a nice 8-pt deer. That pretty much clinched it for me. The thrill of taking a deer that close with my 9410 was awesome. Since then the 410 slug has become quite the hobby for me and I have been trying to find a better (both in accuracy and terminal performance) ever since. The Brenneke slug (modified to work in my 2.5 inch Win 9410) has been the best performer to date.
I am really hoping Turbo1889 gets his heavy weight slugs working though I think some of his designs could take the 410 slug to the next level for use on medium size game.