I picked this up in one of the bin sales at SLICS. It appears to be a brass shotshell with a brown wad varnished in the top of the case and a very thin rim, only .03" thick.

Neck Diameter: .372
Base Diameter: .378
Rim Diameter: .464
Case length: 2.202
Oval brass primer

Headstamp: W 17 at 12 and 6 o’clock

I don’t think it’s a shotshell (it doesn’t rattle when shaken). Somewhere in the back of my feeble mind I recall seeing something about this round many years ago, like it was maybe an artillery primer or something. I did a search here and it came up with 939 matches. Thanks for any help!

sounds like the 110 gr. percussion primer.
I have a W 4-17, a W 7-09, a W.C. 18, and two with only the “W” showing at 12. The 4-17 has a what you might call normal diameter brass primer & it has been struck, so oval before?
The others have either flat copper or flat brass (<-W 7-09), & are about .300" wide.
These do not have a visible neck but appear straight.
hope this is of help.

Edited once to add:

Also with a REM-UMC MK X-8 41 headsatmp a large-rifle-size flat nickel primer. (no body holes)

& that this 110 gr. case is also known with a series of holes in the body as found with larger artillery primers.

Those I have in a draws (or unfinished cases, as no vent hole but with the case / body holes) with REM-UMC MK X-9 41 and REM-UMC MK X-9 39 headstamps.
As loaded with the 9 41 date.

Thank you very much Pete!