Description of a shotshell

Excuse me for this stupid question, but I would like to know the words to describe a shotshell in English and in American language.

Indeed depending of the documents I’ve found (British or US) and depending of the year people do not use the same terms !

Here is what I have read

  1. the rim is the bottom part of the shotshell
    Therefore I say : rim diameter.
    (I have found a lot of documents saying head diameter)
    (I don’t like that because it is confusing)

  2. just above the rim I measure the base diameter
    (people use head diameter or rear diameter or diameter under rim)

  3. on the opposite side of the rim are measured the external and internal front diameters.
    (people use mouth diameter and other forward or front or nose end diameter)
    When they use mouth it is the internal daimeter, isn’t it ?
    And how do they call the outside diameter ?

Conlusion: What are the good terms for:
the rim
the base
the internal front part
the external front part


I forgot also :
some use neck diameter for the front part

J-P - my opinion only. While head diameter is correct terminology, people get the head and the base of a cartridge mixed up - they are not the same. I agree with you that, especially in cartridges that have a rim and do not have the deep extractor groove above it of rimless rifle cartridges, and auto pistol cartridges, that it is ber to call it “rim.”

The rim: Rim Diameter
The base: Base Diameter
The internal front part: Inside-Mouth Diameter
The external fron part: Outside-Mouth Diameter

I am sure you will get other opinions. Again, this is just mine, and if I were writing on shotshells, it is the terminolgy I would use. The only thing I might add would be to somehow describe the brass portion of the case, including the height of the brass and its diameter above the rim, as well as the base of the plastic or paper where it enters the brass portion. I don’t do shotgun ammo, so not sure exactly what those would be called.

Again, that is just the way I would do it. Perhaps a shotshell collector knows of standard CORRECT terminology. In my opinion, some of the examples you cited, and I know they are not yours, but someone else’s, are simply NOT correct terminology by any standard.

By the way, I tend to use capital letters to begin terminology like this. That really isn’t necessary, nor is it really correct English. I don’t know why I do it - just habit. I kind of look on them like titles, as in the title of a book.

JP–I would agree with what John Moss has said. I would add the following:


Head Height–The length of the brass part.

Length–The over all length of the LOADED cartridge. This would NOT include the length of the crimped part.

Crimp–either rolled (over a top wad) or Pie or Star crimp. This is the part that is folded over to hold the shot in.

Top Wad-- a paper, card or plastic disc used in older shot shells to hold the shot in.


Casemouth or Case Mouth–What John called the Outside-Mouth Diameter

Bullet diameter–For loaded cartridges it is the diameter of the bullet as measured as close to the casemouth as possible.



On the first U.S. rimmed cartridges , the rim was called the “head”. That term carried over into the 20th Century but is mostly obsolete today.

That’s where the terms folded head and solid head came from also.

The term “headspace” describes the “space” needed to accomodate the “head”, in other words, the distance from the breech block to the front edge of the rim.

When rimless bottle necked cartridges began to appear there was no rim, of course, and the cartridge seated at a reference point on the shoulder, usually called the datum point. The continued use of the term “headspace” to describe the distance from the breech block to the datum point confuses many people to this day.

Then you have the rimless straight cases, the semi-rimmed cases, the belted cases . . .


Actually, for rimless cartridges, the term head is a much better term - as in “headstamp.” I think the use of the term head is still perfectly valid, but admittedly, in things like speaking of the diameter at the rim, or the thickness of the rim, that word - “rim” - is more descriptive. It is confusing to have different terms for the bottom end of different types of cartridges.

thanks again to you both!