The Marlin 410 has arrived

My Marlin 410 came in today. The action is slick as snot on a brass doorknob. I can't believe how light the gun is, compared to the newer Marlin 410's that were made on the 1895 and it's got to be a couple pounds lighter than the Henry .410 lever action.
This one had some ivory inlays put in, and since it appears it wasn't an original deluxe version, someone had some very nice checkering added.
The real puzzle remains the button on the bottom of the frame that was added. It screws into the frame, the hole is threaded, but it doesn't appear it does anything. I don't know if there was another part or if it didn't work out as planned. It doesn't seem to affect anything when screwed in all the way. I am curious to know why it was done, but there's probably no way we'll ever know.
I picked up a couple of boxes of Remington 2 1/2" #6 shot to pattern next week, and then I plan on taking it to hunt squirrels as God intended.

Can't really see inside that hole. Does anything move or protrude when you cycle the action? If so, could it be a reservoir for a lubricant?

Magazine block? Makes it a single shot shotgun.

That is an interesting looking old piece for sure

I think the cap may have contained a spring and plunger. Just a guess. Why else would it be as long as it is?

As for what it did? It must have been a feeding block to convert to a single shot - as has been suggested.

What happens if you depress the recessed bar and cycle the action?