Has anyone used the rifle inserts for single barrel shotguns? Curious about accuracy @ 30-40 yards; I know it can't be all that much of a tack driver. Could provide an alternative use in a seldomly used shotgun.

At the range you mention, current designed sabot slugs will give you 2 inch group and have big knock down energy.

I don't know in Alabama, but in my country, you can use shotgun to hunt wild boars only and only on group hunts. Every other game and/or situation calls for rifle.

What are you talking about?

Essentially a "rifled" choke tube?

Those were junk in my limited experience.

Or are you talking about a replacement rifled barrel for sabot slugs?

Those work, but are not as accurate as a real rifle. Sabot slugs with them are 2" or so at 75 yards, IME.

I have not heard of a full length insert a'la Briley tubes that are rifled.

If you are thinking of those chamber inserts that you could stick a pistol round in, the one example I have seen was not rifled- it was for .22 LR, if I recall correctly (it was 35years ago...) and with shotgun sights that were not connected to the barrel, accuracy was worse than a conventional .22 pistol. I heard of them for some centerfire rounds, but never actually used one. The one that we played with was like 6" at 10 yards.

It went bang, and was safe. That's all I could say about it. You had to use it in a break action gun and poke the empty out with a dowel...

Useless IME, but that was a long time ago.