Just my 2 cents but I would suggest using a .410 as a .410, period. There's lots of slug and buckshot options.
There are lots of youtube accidents waiting to happen out there, 44-40, 303 Brit, 45 Colt, and 444 Marlin, for your own sake Google some cartridge dimensions.
I had a TC Contender 410/45 Colt and it was great with .410 but a joke with the (lately worth it's weight in gold) 45 Colt and as stated in the manual I had to remove the choke to shoot it, a fraction of the velocity and my kid is more accurate at 25yds with a sling shot.
But speaking to 'older' scatter guns, The Shotgun Book by the late Jack O'Connor lists the following regarding choking for the .410 bore shotgun.
Data include (in order): boring, bore diameter, muzzle diameter, constriction, and percent at 25yds. in 30-inch circle:
Full Choke, .410, .396, .014, 70
Modified, .410, .405, .005, 60
Imp. Cyl., .410, .408, .002, 50
Cylinder, .410, .410, None, 40
Measuring my own Remington Full Choke I found it to be .388" and the Mod .398"
I cut open Federal 000 Buckshot the other day, the pellets were .350" and with the wad .396"
This morning I cut open a Winchester rifled slug, and voila the base is .396".
It seems to me the manufacturers are attempting to save us from ourselves when it comes to shooting anything out of a full choke .410.
That being said, worth pulling out the calipers before you try slugs. Safe shooting everyone.