Help: ID this tool/die

I got this thing in a recently acquired trove of reloading stuff. It was in a zip lock baggie, no brand info. The coarse threads are the 7/8"-14 pitch of reloading dies, I don't know what the fine thread pitch is. The thinner part has a sort of funnel internal shape. The orange stuff is rust, it was in a shed for more than ten years before I got it, and it'll be boil converted.
Thanks in advance.

alfsauve said:

Looks like a seating die, but I can't see what's on the inside looking from the bottom up

Click to expand...

I wondered about that, but there's no seating stem. Something could clip to the restriction in the neck.
Here's a pic down the thing:

PRD1 said:

The die is for the Lyman 310 hand tool, useable with the Lyman Tru-Line presses as well. The adapter ring is threaded 7/8 - 14, to allow use in standard reloading presses with that thread size. Normally, the Lyman dies are marked to indicate type and caliber.

PRD1 - mhb - MIke

Click to expand...

Thanks, that narrows it down a bit. I can't see any markings on it; the rust isn't so bad it'd obscure writing. Hmm...

Bazoo said:

That is a drop tube for a Lyman 55 powder measure in a press adapter.

Click to expand...

Thanks.
Having now looked at a picture of the Lyman 55, I can see that the thumb screw on the side near the bottom would turn into the constriction at the neck of the thin part, locking it in place; not a bad way to go.
I haven't seen a Lyman Powder measure in all the mess of stuff, I'll have to dig a bit to be sure.