Someone else asked something similar not long ago (although without the double barrel mention). Same answer.
I don't know why, but apparently there is some confusion. ALL the .45/.410 guns are
NOT .410 shotguns that can fire .45 Colt ammo. They are .45 COLT gun that can fire .410 ammo.
Thompson Center came out with the .45Colt/.410 barrel for their Contender a long time ago, and my experience is that it is a fairly good compromise, BUT BOTH rounds suffer in their performance.
.45 Colt's long bullet jump in the .410 length chamber often (not always, but often) means accuracy isn't as good as a standard .45 Colt barrel. I can prove this if you like, your gun may be different, but I wound up getting a separate .45 Colt (only) barrel for my Contender, as the .45/.410 just wasn't as good as I liked, in .45.
In .410, the shotshell suffers from a degraded pattern, compared to the smoothbore, because of the rifling. The "straightner" section does help, but patterns are still below par compared to a true shotgun. The real "advantage" to a .45/.410 gun is that you have a .45Colt, that with a simple change of ammo, works passably well as a short range shotgun. The factory .410 shell simply works better as a shotshell than a handloaded shot charge in a .45Colt case. And that's about all it does.
A compromise, but useful is some situations. .410 slugs are pretty zippy numbers, and there is some promising power there, BUT, being what they are, accuracy isn't up to rifled gun standards. You may get a degree of precision from any given shot, but you just cannot count on it, being a subcaliber slug in a rifled .45 bore.
The current market interest in the Judge (and its copies and variations) is, I think, a bubble, with most buyers either not knowing the full reality of what it is that they are getting, or worse, believing the BS about "not being able to miss" with a shotgun.
IF Federal laws allowed it (technically, they do, but its a cumbersome process), a handgun size shotgun (smooth bore) would be an awesome, and effective piece for many situations. SO we are handicapped by the decisions of our political rulers as to what is, and is not "suitable" for us to own.
So we get a handgun that as a shotgun, isn't as good as it could be, and not quite as good as it could be firing standard bullets as well.
Generally, shotguns are not built to stand the pressure of even a moderate handgun round. Action design just isn't up to that, in most guns. And in the older guns, sometimes the materials aren't up to it either.
Although it does bring up the idea of something like a Winchester model 42, reconstructed to manage .45 Colt......It wouldn't be simple or cheap, but it would be interesting...especially solving the feeding issues....
