This is a brief look at the 410 adapter. This one is steel and cost me 15 dollars.
It works well with plastic shells. Fires fine, Extraction is easy. There seem to be slight imperfections that when you shoot a Russian steel shell the shell expands and was not easy to get out. The 3 00 pellets from the Russian shell patterned inside a paper plate to my surprise at 25 yards.
Notice the rings? It took a sharp blow with a metal rod inserted to get it out.
I tested different choke tubes-no choke (out of the DE), modified, and turkey choke (out of the 870). The only one that would put enough pellets into a small game zone at 25 yards was the turkey choke. At 15 all of them still had a dense enough pattern to put down small game. I shot several patterning targets put the .095 holes don't show up well on camera... At 25 yards it's pretty much a half a door size pattern, with the turkey choke throwing it more dense to in my opinion allow it to be used for small game at that distance.
Since the adapter is quite short (this one is three inches). Pressure drops off pretty quickly. This leaves burnt gunpowder in the barrel. Depending on your use, good or bad.
In my experience, this adapter (3 inches) will not cycle in my pump gun-from tube magazine to chamber. It needs some slight help on the shell lifter from my hand. My 870 is made for 3 inch shells. If I just work the pump back and put it in through the loading gate, it works great.
On the other hand, the 20 gauge adapter I have is 2.75 inches or so, and that will feed from tube mag to chamber with a brisk motion.
However, I don't really recommend this, as you are relying on friction fit to keep the shell in the adapter and in a pump gun the shell could slide out of the adapter and leave you with a nasty mess.
If you set up your pump gun as a "scrounger" with scrounged ammo with 2.75 inch adapters, and wanted to cycle through whatever you had, and very desperate, I might put a tiny bit of superglue to keep the cartridges/shells in the adapters for reliability. Having to take a sharp blow with a metal rod to get the spents out of the adapter a second thought to putting lead in the air. Not recommended.
Out of my single shot, no complaints obviously. The adapter works great. Drop it in and fire.
All in all, the 15 dollar 410 adapter works great. Choke is a big deal if you would intend to use it on small game out to certain distances.
Why would one want to own such a silly device? Why not I say...
Allows you to carry lighter 410 shells.
Cheap in my opinion, 15 dollars.
Scrounge-ability is a plus if necessary. Most people ignore a certain aspect of firearms. NOISE.
Seemed good but next one not so good
???? I'll have to shoot another one to see.
And for some reason I was having some interesting patterns that make me question my statement about it being used out to 25 yards on SMALL game with the turkey choke.
Here's what I mean.
It appears the modified choke is throwing a tighter pattern than the turkey choke. hahaha
The overbore concept seems pretty much spot on in my limited tests.
A slightly smaller gauge with adapter will pattern pretty good. Going from extremes 12 to 410 maybe not as good (compared to the 20 out of 12) with shotshells.
I don't have a 20 gauge to test a 410 adapter, but I'm betting it would pattern better than shooting a 410 out of a 12 gauge.
The 20 out of the 12 was pretty good. Good enough for me.
Keep that in mind-overbore
It does seem that the 410 throws a longer narrower and hence tighter pattern out of the 12 gauge rifled barrel compared to the 20 gauge. However, at 15 yards I can't recommend it for small game. At 7 yards, yes I can recommend it.
I also just for the heck of it shot some 410 slugs through the 410 adapter. because they don't even touch the adapter at all accuracy was VERY bad. 7 yards, 1 shot hit the plate. Might get lucky if a predator swallows your muzzle, other than that not so much...