Help ID'ing Unusual Artillery Shell Casing

I would appreciate some assistance in identifying an artillery shell casing. The shell in the images measures approximately 93-95mm inside the case mouth, there is some distortion to the mouth so it’s hard to get an exact original dimension. The shell casing has an OAL of 300mm. The case has little to no taper. It has no markings anywhere.

The case has a stepped, convex head and what appears to be a very small belt just forward of the case rim. Hard to describe the unusual case head, but it’s shown in the photos. The case has a primer pocket, but no flash hole. There is a crack in the primer pocket that does not go through to the inside of the case, which is odd, but may be due to a crack in the forming die which has been impressed into the primer pocket. It has obviously never been fired.

My guess is that this shell case was removed from the production line as a reject due to the primer pocket crack, hence no head stamp. I assume that it was made/designed for a screw-breech gun since the convex head would seem to be difficult to adapt to a sliding breech. It may be for a gun that was developed but never put into production. I’m hoping someone on this forum can help me identify the shell and its intended gun. Thanks.

No expert on shells but I have a few. I suspect that closed primer pocket was done after the shell was fired and discarded to make it useful for the next owner to hold things. All the shells I have either are open at the bottom or have a long tube coming up that allows for the powder to be ignited uniformly. Primer was probably removed from this and then sealed.

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Originally Posted by Aragorn243

Primer was probably removed from this and then sealed.

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I don't think so, it hasn't been finished. This would have been drilled and threaded to finish. I don't even think the crack matters, that would have been drilled out. I'm wondering if this hasn't been finished at the base yet? Thus the convex shape? They get a final turning to make things flat, see a base of a new round and you'll see the turn marks.

I wonder if it was to be an 18 pounder? Still needing a final trim and a bit of taper in the size die, also the rim is about right...length is just over and outside would allow for the size down... ‎84 x 295mm R is the 18 pounder case size.

I know there's enough guys here have them, maybe we can see if one will measure things out?

Aragorn243 - I don't think the primer pocket has been filled in. It rises about 10mm from the bottom interior of the casing and, even though my photo doesn't show it, the metal in the interior is of uniform finish throughout indicating no visible glue, solder or filler.
Thanks for the comment.

browningautorifle - The observation that the case is similar to the 18pdr is a good one - and I really hadn’t considered that it could be an unfinished 18pdr. The head of this thing is dimensionally very close to an 18pdr, with all dimensions on the subject case being just slightly larger than the 18pdr. I never considered the fact it may be an unfinished 18pdr case since the case mouth diameter is 10mm larger in diameter and I assumed the stepped head was part of the case design. I have seen small arms ammo that has a "domed" case head several steps prior to final finishing, but not with a "step". Even the interior primer pocket area is similar to the 18pdr. I must confess I have never seen an artillery shell case in the various stages of forming so I don’t know what they look like before completion, but your explanation seems to be the right one. I have taken a couple photos next to an 18pdr and you can see the similarities.

I’ve had this shell case within 6 feet of an 18pdr case for 15 years and never made the connection. Thanks again for your insight.

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