Markings INSIDE of a 105MM tank shell case

I recently sectioned a steel 105MM M115B1 shell case and noticed something I have never seen or heard of inside. Located inside on the very bottom, next to were the primer tube extends are three good sized letters engraved in the metal. They read, “PRM”. Anyone hear of this before? What does PRM stand for?

I took a photo which did not come out all that great but you can still vaguely see the PRM at the 12 O’Clock position.



I’ve never seen such a thing either, but then I must also say that I’ve never really looked.

A better question is how did they stamp it? As a part of the drawing process?


I just looked at some of my other 105’s and one more of them also has markings on the inside. It has letters and unknown (to me) symbols on the inside. Maybe they were stamped before they were drawn like you said?


I have sent the question (and this link) to a large caliber manufacturer. He said he can venture a quess, but will turn it over to the real experts. I would expect an answer shortly.

Awesome! Thanks so much for that Pepper. I am going to try to photograph the markings inside the other 105 I found. It has allot of symbols inside. I hope they photograph ok.

Thanks again Pepper!


Here is the definitive answer, from our friends at GD-OTS, General Dynamics and Ordnance Tactical Systems (and they are,

Pepper - is the billet actually made by the same company that forms the case itself, or are the billets identified that way because they are supplied by an outside maker? I know that some case makers start from scratch, and others by the brass discs, etc., that are then formed by them into cases and bullet jackets, etc. Just wondered. Not my field, but interesting. Many small-arms ammo cases have interior markings also, but not sure which ones other than some British .303s. It is an interesting subject.

WOW! So happy to learn “THE DEFINITIVE ANSWER” on this! I was super curious about the markings when I discovered them. Thanks allot Pepper! Very grateful to you and your friends at GD-OTS for your help. I am going to hunt for more internal markings. Unless the case is sectioned, I can’t seem to get quality pictures of these markings, bummer.


My thanks also Pepper. Great information!


Just looked down the inside of my 5" 54 case. Noted a “3” and a “7”. Maybe some others there, but 30+ years of dust, plus being a fired case, makes it difficult to discern any other markings. What a find, Jason. And Pepper’s help is priceless. May send him my double-ended pen flaregun as a reward.


But I’m guessing he already has a dozen, new in the box, with assorted flares. Oh well. Thanks for your efforts, nonetheless.

That flare gun is awesome Rick. Very cool that your 5" case also has markings in it. What do we call these markings? “Reverse Headstamps”? :-) haha



Too funny! I am finally known for something :-) I bet they must have a technical name? One of the markings in the other 105 case looks like a small zero inside a enclosed horizontal oval ( o ) .

I love that Pepper was able to call a manufacture for the details on this. It would be cool to have a blank of a large caliber shell before it is drawn. I have seen a few members post photos of a sequence of manufacturing development of drawn smaller caliber cases. Very cool stuff. Is their any footage of this process being done online?

Some WWII German artillery projectiles (7.5cm and above) can be found with markings stamped inside them, on the side, both Army and Navy projectiles. These markings (at least the ones I’ve examined), consist of the manufacturer’s code, lot number and year of manufacture. This is especially useful when the outside of the projectile is pitted and the stamped markings are gone. I’ve seen it on (in) HE, Hollow Charge and Illumination projectiles so far, but these internal stampings don’t appear in all projectiles of these types. What the purpose was is a mystery to me.


The process of drawing big bore casings is not very different from small caliber. Steel casings however are a lot more difficult to make. There are several inspections during the process.
I will sent Jason a part of ORDP 20-249 section 6,manufacture of metallic components of artillery ammunition. Jason could you please post a short and easy to understand extract.

This in from GDOTS last evening in response to John Moss

The cartridge case for the German monster gun “DORA” 800mm siege gun has a Jasonstamp inside. Years ago Ian Hogg stated in one of his books that they were only marked that way. He was mistaken. The example at Aberdeen has a typical headstamp which has been wasting away for years. I doubt that Ian ever turned one of these up to look at. It is quite a task.

The Dora case has got to be intensely heavy and hard to manipulate. Your “DORA” thread was one of my all time favorite threads in the forum. Those big guns are incredible engineering marvels. I wonder how many cases use these internal markings? I have looked at all of mine and not every case seems to have them. Of course they are not easy to see if the case is filled with gobs of dust and dirt like SlickRick said :-)

I checked all 5 of my brass ca. 1940s and 1950s US Navy cases (3" and 5") and none have any marks whatsoever.

Maybe it was an Army thing? You know how the Army is really anal about keeping track of EVERYTHING. :) :)


My 5’’ 54 is from the early '70s. Sadly, the original stenciling is gone. Having had a pair of these on which to place my stereo speakers (Bose 501s), they were something of a “centerpiece” in the living room. They were sooooooo tacky, what with having been fired and stained/charred accordingly, that I was obligated to PAINT them (pre-collecting days). Now I’m down to one. And I’m still messing with it to see any other numbers. Not much room at the bottom to move around or clean. May need a partial sectioning and paint job to find MY JASONSTAMPS. Sorta like having a planet named after you, or something. Way to go, Jason.