12 gauge cartridge

Any idea what it is and why the body less wide closer to the head?

This case looks to have been made in a basic workshop on a lathe.

It was probably made slightly too small and was blown out when fired in a standard 12 gauge chamber.


I agree with Falcon, you can see the tool cutting marks this was done on a lathe that did not have automatic feed.

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Is the head end screwed onto the tube part, as there appears to be a joint in the case?

Sorry, not screwed onto it, it is a solid piece. I think it is correct that it is a lathe work, very fine one. The bulge is probably fire formed, it is only on one side, the other side is smooth and normal, see my pics below, I’ve rotated the piece to show the bulge. Why would anyone make it, a lathe excercise?


"I think it is correct that it is a lathe work, very fine one. "

Ugly work I would say !

" Why would anyone make it, a lathe excercise?"

if it is an exercise the notation would be 2 or 3 on 20.
it was rather made by somebody who doesn’t know how to use a lathe !

And the fact to have an automatic feed or not changes nothing.

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Sorry, don’t know too much about lathes, maybe it is a coarse work. But it was made to be fired, there is a primer, and it is hit. Why would one make a common calibre like 12 gauge? And then it is fire formed in a very strange way!!

it is a brass case, therefore the guy can reload it many times.
Interesting if he has no paper to buy loaded ctges (in many countries you need to have papers to buy even shotshells) or if he wants for example a light load (modern shotshells being too hot for his gun) or if he wants to load them with black powder because he has and old gun.
therefore many reasons why he could need this kind of shell.

the fact the case is badly altered could mean either the shell is not at the right dimensions, or the chamber is not good.

Give me the diameter just above the rim and the diameter where the case is enlarged.
We can check if the case he made is correct.

And do not forget this shell was not even fired in a gun but perhaps in some engine he made with tubes and so on

If the case is normally made the walls are thicker close to the rim than far from the rim.
You can check the design of the inside he made


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There are various reason as JP said;
1). It is quite possible that the case was made for one gun and has been used in another.
2). Made to suit a 14 bore and used in a 12 bore (or similar sizes even though stamped 12).
3). Poor workmanship at manufacture and was just manufactured undersize.
there are other possibilities but they are probably the main ones.

I would think if you check the inside you will find that the case wall ends approximately where the bulge starts and the internal base of the case starts.
You would probably also find that the wall thickness is thinnest at the area of most swelling, force will always find the weakest point.
It could also be that the cartridge sat at the bottom of the chamber as the gun was closed and the only room to expand was above case.
Perhaps the chamber is actually incorrectly machined and is oval, this would also force the swelling to one side.


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Thank you both. There is a solid internal brass head of 9mm above the rim which corresponds to the beginning of the bulge at 9mm on the outside. I’ll post all the measurements tomorrow.

Out of interest, this is not the first time I have seen this, a friend of mine had an 8 bore that had miss-shaped chambers (they were a bigger diameter a third of the way up the case). He had to carry a cleaning rod with him when he used it to get them out after firing as they stuck in the chamber.

I made a series of dies and resized them for him.

The picture was taken after resizing.

Here are the measurements.

Your sizes confirm that the cartridge is certainly under size and after swelling is over size.
Based on a standard 12 bore chamber being 0.800" at the mouth and 0.812" at the start of the forcing cone. (Sizes given are for a standard 2 1/2" chambered gun). The difference for a 2 3/4" and 3" chambered gun only decreases by 0.001" and 0.002" respectively with the mouth size being constant at 0.800".
With out knowing what it was fired in I doubt you will ever know the complete answer.


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