A big thanks to so many who posted in a myriad of threads in the past. A friend picked up one of the 45/410 pistols this summer and has not seen a .410 shell since. I searched through the site and was able to cobble together enough insight to load some of my 444 Marlin brass as 410 shells for snake control for him. I don't reload shot shells so I had plenty to learn. Thankfully I have a neighbor who gifted me a couple pounds of 7.5 shot to experiment with.
As the threads recommended, I started with the brass un-sized. I tried both both pistol and rifle primers and found his pistol had a hammer spring more than capable of setting off a rifle primer. Both types of primer fit the brass and there was no perceptible difference in performance in the first test.
Because the plastic wad isn't a real snug fit for the brass cartridge I decided to use a wad under it. I had none on hand so I opted to make some cardboard wads. I drilled the primer cup out of a 45ACP brass, assembled a screw and nut in it so I could chuck it up in a drill, beveled the brass to sharpen it, then used it to cut wads from the stiff back of a tablet. Cutting them against the end grain of a 2x4 clamped to the bench was fast and easy. The wads ended up just under .450" and fit the 444 brass nice and snug.
I don't keep too many powders on my bench so I spent a while looking for a suggestion using what I had sitting there. I opted for 4 gr of Unique under 1/2 oz of shot. I know it doesn't sound like much, but against a cardboard box it makes a fair pattern with a ragged hole in the middle, and some pellets exiting the back side of the box. That was at a distance of about 15'. More than enough horsepower for a snake load. One of the thread entries I saw mentioned that the lower power loads tended to have better patterns out of pistols. I wondered about pressures, but since the gun was made to handle 45 Colt rounds it would easily hold up to this load that was less than the recommended starting load. With 4 gr of Unique under a total payload of about 230 gr, this was in the powder puff range.
Anyway, an un-sized 444 Marlin brass, a large rifle primer, 4 gr of Unique, 2 cardboard wads over the powder, a plastic shot wad and 1/2 oz of 7.5 shot, another cardboard wad over the shot, and then a light roll crimp on the brass. I was tamping down the wads with a piece of 5/16 dowel as I went. In case you wonder about such things, firing the round straightens the roll crimp out of the case mouth so reloading is quick.
So far I haven't bothered with anything more than the snug fit of the over shot wad to hold everything in place. It's such a light load that there's no recoil to jar things loose. I'll do some testing and see if the over shot wad moves at all. I can add a little glue if it does. Otherwise, the only other add to the recipe will be a little bullet lube poured in the end of the case to seal the round and protect the over shot wad from the elements.
Again, thanks to all who put their knowledge out there. Without the conversations in the threads on this site I never would have tried this little experiment.