Shot shell external corrosion


What are these calcium looking buildups? I cleaned the one on the left. And it appears there is no cartridge wall breach (no hole). They are all live “REM-UMC No.12 Best” headstamped.


The closing wad on these looks more like a thick liquid type sealer than the cardboard wad with load info which would normally be used on a shot load.

These may be some sort of special purpose load with some sort of chemical reaction between the contents and the brass case.


Look to be tear gas loads & I’ve no idea what part of the chemical mix is breaking down to cause this, but it’s not an uncommon happening.

In my experience once cleaned off it doesn’t come back, for at least a long time (no end date that I have experienced)


Possibly the cases were contaminated with small amounts of the filler material while being loaded which caused the corrosion, and after that is removed it should not reappear?


Hi John
Judging from my collection I think must migrate through the brass, because it doesn’t appear until the rounds are old. I further think that once it’s had a reaction, it’s done reacting & so when cleaned it doesn’t reappear for the limited foreseeable future.

All this is just my 2¢ I have no paperwork or data to back it up.


Agreed an “irritant” (tear gas) powder load. I have no good idea of the mechanism or cause…but in my experience; rounds that have been subjected to a damp environment have this type of corrosion. A bit odd/rare to see the top wad/seal in such “like new” condition. JMHO


Adding more visuals for more guessing. These 4 were in a bag with a mixture of mostly modern pistol ammo. So no boxes or extra info.


Hi Vlad,

These are Hercu-Gas tear gas shells loaded in the 1930’s by Hercules Gas Munitions Corp., Chicago, Illinois.




Fede, much obliged. Do you think they still work? Were they made for police or military?


They were made for billy clubs intended for police use, but they also loaded smaller cartridges (.410, .38, .32) for pen guns offered to the common public.


One more “thank you”, here is a video


Interesting topic (so forgetting the type of cartridge from my reply for the first part).

  1. Firstly I can not remember seeing any as bad as that before (assuming they have been kept indoors).

  2. Secondly, like Pete I have never found any that penetrate the case wall.

  3. Third thing I noticed is there are two completely different types of corrosion that occur. The first is completely random and the second is in very specific places.

So the first could be specific to the contents of those cartridges and I have no way of being able to prove or disprove that.
What causes it, some thoughts;
Random spots as found on numerous cases (loaded or not) could be from basic chemical reaction (the zinc in brass is what primarily decays).
What causes the zinc to decay? ammonia and mercury are two of the main causes, there are various others. However the two mentioned are found in both caps and powder. More so in older cartridges, also not knowing the composition of tear gas, that may be why the corrosion is so server on those cases?.
The composition of the brass and also how good a quality it was will also have a major part in the decay of the said cartridge case.

I have attached some pictures of some brass 10 bore ejector cartridges these would have been loaded in the period of 1920 - 1928, they came out of a full box and have had almost no handling (just me taking them from the box, “I believe”). When you look at the cases you can see quite clearly that the corrosion is in two bands. These would be roughly at the top and the bottom of the wad or the cards on either side of the wad, rather strange.

After taking the first photo I thought to add one more to show the Over Shot Card, for the reason I noticed that there is also a visible line of corrosion in that area too, although not as pronounced as the other two places.

Closer view of the lines of spots.

These areas lead me to believe that the fumes/vapour from the contents are getting concentrated at these points and then leeching through the metal!

Well that’s my take on it.


Or, the bands may be the result of external contamination on the case from some of the rollers or sorting machinery during manufacture and packing.


These spots are caused by smokeless powder breakdown. Nitric acid is used in the making of powder & when not properly washed out it does this over time and in the right conditions.

The reason for two rings on is these is they are packed nose to head so the touching from one over-powder wad generates a spot on the next, even though the over-powder wad is not placed at that point.

Not sure why the corrosion is also at the crimp, it may be that some of the original ‘flakes’ may have come loose and fallen off to contaminate those areas also. I do see a spot on one rim & at the mouth / petal on another.


Could acids in the card wads themselves be another possible cause?


Certainly possible, but the over powder card is relatively thin, & so would / should have little acid in it. The cushioning wadding is much thicker so it that was the source, I’d think the effect would be much broader.

I’ve seen the type of corrosion on centerfire rifle, the why I am pretty sure of the cause. if you carefully remove it the colour of the underneath brass will be pinkish.


The theory of print through from one case to the other is certainly not the probable cause of the lines of corrosion on the 10 bore cartridges above, there are various reasons why this is highly unlikely but the most significant is they don’t match up with each other by about 0.150" (circa 4mm).

Two cases laid nose to tail for comparison.

I am wondering if the surfaces of cards are acting as a collector (sponge) for the vapours and therefor giving a band of concentrated “what ever” to attack the case wall.

Having just got back home from a day out. I have dived into the brass cartridge cases, I am talking ones where I have large quantities of the same cartridge from the same box/brand/era, and manufacturing/loading time.

I will do some more pictures tomorrow.


Nice Mike, shoot down my perfectly good theory. First time this afternoon !

Be interesting to hear what you find.

Falcon may have been on the right track !

If you have others that exhibit this same ‘look’ & if not too valuable perhaps one could be disassembled?


As promised, here we go;

First up are some Nobel brass “ejector style” cartridges. These are paper lined and came from a plain (no markings) 100 box, so I would assume shop loaded.
Note, the corrosion is slightly more random although a trend can be seen for concentration of the spotting at the “estimated” position of the wad/s and any over powder/under shot card. In most exhibits I have taken two pictures for clarity.

Next up are some Kynoch brass Grouse Ejectors, again a paper lined case and I would say factory loaded.
These exhibit no signs of corrosion anywhere.

Next some Eley Nobel brass cases, same era as the 10 bores first shown but from a different supply.
These do have the same marking on the case but to a significantly less pronounced affect and on some cases it is almost impossible to find any.

Next are some Kynoch Patent Brass Ejectors, probably shop loads and again the original loads I suspect, rather than factory loaded.
These are purely brass cases and have no liners. I could only find one spot in all the cases I picked up (second case from the right). There are some cardboard box stains just visible on some of the heads.

Next, Eley Ejectors, again these are a paper lined brass case. Factory or Shop loaded.
The corrosion on these is very random but if I was to be hyper about it I would say there is a slightly more intense concentration in the area of the wad!!
After putting the cases away and looking at the pictures the second case from the right “may” have a hole that penetrates the brass.

Just to show how inconsistent it is rotated the cartridges 180 degrees and took another picture.

As a base line, these are plain cases never loaded (NPE’s) no corrosion marks of any kind, just cardboard marks from the box on some of the heads this also appears on some of the case mouths.

Close-up of head “stain”.



Just to show what a buff of first fine steel wool and then of fine bronze wool does to the corroded rounds like this.