Here's my take on .410 slugs - back a few years ago when Indiana had yet to have a 'rifle' season for deer, my kids were too young and small to handle a full-size 12 gauge slug gun, or even 20 gauge slug gun, and I honestly feel that a muzzleloader is dangerous as a 'first gun' for hunting (matter of opinion, I know). They were also too petite and young to handle a .44 Mag or similar handgun legal for deer.
So..... the only other 'legal' option was a .410 using slugs (yeah, I know...

).
I looked at the 'power' of the typical .410 slug, and it equated to the 'vintage' level of .32-20 loads - perhaps a fine load for an experienced hunter/stalker, but hardly the best for a novice.
I actually purchased a .45 Colt/.410 Handi-Rifle with the intent (shhhh... don't tell anyone...

) of
violating the law, by having them hunt with a ".410 shotgun", yet use .45 Colt in it. My RULE for whatever they hunted with was something along the lines of "You have to hit 4 out of 5 pop cans off the bench at 75 yards, and 4 out of 5 standing at 25 yards", and they COULD do that with a variety of ballistically legitimate guns (Marlin .357 Mag, Marlin .44 Mag), so I figured put a scope on that Handi, and they'd be good-to-go...
.....NOT.....
It wouldn't group inside of 24 inches at 25 yards...! I tried everything from 'cowboy' loads, to "+P+" loads, and even thought about slipping a .454 Casull in. Nothing worked well, probably because the bullets had keyholed before they hit rifling.
So, project abandoned.
Why it is pertinent to THIS thread is because my OTHER thought was to have them use a chamber/barrel insert in a breakopen 12 gauge, using .44 Mag or similar ammo.
My "rationale" for all this was that I would be hunting with one of the following:
- 12 gauge slug gun with saboted 240 grain '44' bullets around 1700 fps, or
.50 cal Muzzleloader with saboted 240 grain '44' bullets around 1800 fps, or
Ruger Redhawk with non-saboted 240 grain '44 bullets around 1200 fps,
So somehow it seemed that launching a 240 grain '44' bullet around 1500 fps was not considered inhumane nor dangerous - the only difference was the firearm used.
Someone makes .44 Mag (and other) inserts for 12-gauge shotguns that include about 12" of barrel (longer than my Redhawk, and no 'cylinder gap'), and a breakopen 12 gauge is light and handy, and I doubt kicks as much with a .44 Mag fired from it, as with a 7/8 oz. Brenneke.
Dunno about .410, and of course the 'barrel' type inserts would likely have to be .30 caliber or less to get much material for a barrel, but if you were willing to have a smoothbore, lots of options come to mind.
I can't imagine the 'insert' has to be all that strong, either, due to being contained in a chamber already (firing a 65,000 psi round in an 'insert' in a .410 chamber would not be something I'd try, however, even if there were no barrel and hence vastly lower pressures.