Is it safe to fire 45 long colt from a 410 shotgun?  I am not asking for plus p ammo but maybe cowboy action type ammo.  I see it being used for those Judge revolvers.

Iraqveteran8888 did this thing with an old 410 single shot shotgun they called "9 Lives" firing an amazing amount of calibers out of it before it died.

Not recommended but proof of concept

https://www.youtube.com/watch?v=BwKydDPY8Xo

.45 Colt is .452-.454 depending in the gun. .410 speaks for itself. Even in a cylinder bore the .45 colt is way too big.

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 25 yds. 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

In a full choke the muzzle is .396 for a .410! That is squeezing a .45 caliber bullet down smaller than a .40 caliber. The way the .410/.45 Colt combo guns do it is with a bore for the .45 colt and a deep enough chamber for the .410.

I would caution very strongly against shooting .45 Colt in a standard .410 barrel. I've heard of people doing it. And I'd say everything would be ok right up to the point it isn't ok. Then it would be very bad.

As above BAD thing to do.

The .45-.410 guns are specifically made to shoot both and the bore is sized for the .45.  The .410 shotgun was never intended to fire the .45 Colt.
.410 shotguns tend to have tighter chokes which restricts the bore to unsafe conditions for a lead pistol bullet.

The .45 Colt operates at 14,000 psi.
The .410 in a 2 1/2 inch load operates at 12,500 psi.
The 3 inch .410 is 13,500 psi which is close, but still over what the guns are made for.

This is one of those great ideas that aren't so great in the Real World.

I have a .410 handed down to my son from his maternal grandfather.  It is marked .410 & .45 colt.

This was more common 70 years or so ago on the store brand .410 single shot guns to also chamber .45.

Now... not so much. So... using "modern" specs on barrel/choke are NOT "what they used to be", when .45Colt was "ok" to use.

Choke specs now are tighter for better patterning.

That is nice. What make is it? I'd like to find one of those.

It is a few hundred miles away!  Back-in-the-day there were "store brand" firearms.  Sold through Sears, Montgomery Ward, Western Auto... etc.

They may all the same manufacturer for each of the stores, but they would roll mark with the store name. Very common prior to the Gun Control Act of 1968.

Many before that date did not have serial numbers... as they were not required by law prior to that act.

I have no clue where to tell you where to start.  Maybe gunbroker, pawn shops, estate sales, garage sales... it will be a Where's Waldo quest... but they are some still out there.

Good Luck