The three most serious reasons handgun shot shell are all but worthless, including true 410 revolvers are 1) velocity, 2) shot size, & 3) shot quantity.
If you buy shotgun shells, you will find velocities from 1155 fps on up!
If you buy CCI handgun shot shells you will find #12 shot and quantities of 1/10 to 1/4 ounce!
I have done extensive firing and pattern testing on 410 hand guns. I learned that the 2 1/2" shot gun shells are 1200 fps and In small shot sized (#9) They make a 6 to 8 foot pattern at 10'! #6 shot , patterns about 4' @ 10' and #4 shot patterns 2' @10' and lastly 000 buck patterns 4 to 6" @ 10'! Between the rifling and velocity, The shot pattern is just pushed into a big worthless ball!
My solution: I made cases that were long for the caliber by trimming back longer cases. I used 460 S&W cases trimmed back to the length of a loaded 45 Colt cartridge, (1.51") the case needs to taper in just like a regular bullet, I used a 44-40 sizing die (38-40 works too) I used the primer and powder gharge for a 220 grain bullet at 700-750 fps (a typical Cowboy Action load). WLP primer 6.7 grains WW231 and 220 grains of #7.5 shot (220grains=1/2 ounce). I use a 45 caliber fiber wad on top of the powder and another on top of the shot. Then I seal the case mouth with any elastic sealant. Bathroom tile sealer works, but I use Gutter Seam Sealer. I use a popsicle stick as a trowel. Smooth the 1/10" sealant level and smooth. Allow to cure! (10-20 days!)
The above shotshells pattern 12" at 12' and are very effective to 25'. I would have sworn testimonies from the Copperheads, but neither living or dead, snakes can't write or type! The guns I used were 5.5" 45 Colt Ruger Vaqueros and a friend was using 7.5" Colt SSA.
Ihe 410 handgun I use to own was a 4" two shot derringer by Cobray (the old MAC-10 people).
The cases are completely reloadable and have yet to require resizing. These cases will cycle in lever action rifles, but the range limit will still be 25 to 30 feet (so no skeet shooting, sorry).
The next batch I make will be with full length 454 brass and will hold 7/16 ounce of shot.
Ivan