In regards to the Judge and the Governor, I know that both the .45 Colt and .45 Automatic both have an enormous gap to jump before they hit the rifling, and this does cause deterioration in accuracy and velocity.
Compared to what? The Judge and the Governor are just like other revolvers in that they will have a specific load that will work best with them. I have the Ruger Redhawk .45 Colt/ACP and factory FMJ .45 ACP shoots horrible, but my handloads using a 200 or 225 grain .45 Colt bullet with 5.5 grains of Bullseye and a roll crimp, it shoots really good, probably equal to .45 Colt and while the jump isn't as long as a .410 revolver, there is still a jump.
I think the biggest detraction for the Judge revolvers is the sights, they don't make accurate shooting easy. The Governor has better sights, but I've not followed how .45 Colt shoots in that gun because I generally don't see people shooting them off a rest using handloads that they've tuned for their gun.
If you want to see what accuracy a Taurus Judge is capable of, follow my thread:
https://www.thehighroad.org/index.php?threads/accurizing-the-taurus-judge.876365/
I'm going to be adding to that thread in the coming weeks and months, hopefully years, as I test different bullets, powders, and in .45 Schofield and .45 Colt cases. I can tell you I was a good 20 yards away shooting 8 inch round plates with .45 Schofield going a bit under 600 fps with no problem.
I also know that when these first came out, there was absolutely nothing on the market in regards to "defensive .410 usage". Everything was simply... run-of-the-mill shotshells. I know a few companies have introduced ammunition specifically for these revolvers, namely Winchester and Hornady come to mind.
Do these respective ".410 defensive" shells actually do anything to increase the defensive capability of the .410 loading, or would one be better off with loading either .45 cartridge in these revolvers ?
Asking for a friend's father who recently purchased a Judge, and for my personal curiosity.
To answer this question, the specialized ammo, it depends. I do not like the Winchester PDX1 because I think the BB's they put in it are useless and often spread so fast they miss the target entirely. The disks look like they work fine and are pretty accurate, but until Winchester makes a PDX1 that only uses disks I wouldn't buy it.
The Hornady Critical Defense ammo is best used in a longer barrel .410 and not a handgun. Accuracy just isn't there. IDK what Remington is offering for a .410 defense ammo, but Federal has 4 pellet 000 Buck and that stuff works fine and is probably the best .410 defense ammo for the .410 handguns.
Is it better than a .45? For inside the home I think the distances are close enough that the .410 Federal ammo will work better because of more wounding capability and at 5y the spread is not much. Across a room or down the stairs and it'll work.
It's when you're shooting 10y or beyond and the pellets spread too much to be effective. I would suggest make the first two shots .410 Federal and the rest a .45 Colt JHP, one that's proven to expand from a Judge/Governor.