US caseless cannon ammunition

The photo below shows three caseless rounds: on the left, a 20 x 87; in the middle, a replica of a telescoped 25-30 mm (difficult to make out the calibre); with a replica of the Japanese 40 mm Ho-301 for contrast. I am fairly sure that the first two are US developments: does anyone know anything about them, the programme they were part of, when that took place, any performance data of the ammunition or gun?

Thanks for any help.


Some information on a 20mm caseless is mentioned in:
(DTIC 239174.pdf)


"Research on development of combustible cartridge cases for small arms was conducted in Germany during World War II. Subsequent to the end of the war, work on combustible cased ammunition for small arms was conducted in Spain by the Belgian firm of SIDEM International under contract to the European Office of the U. S. Air Force Research and Development Command (2). Both 7.92 mm and 20 mm combustible ammunition , capable of being fired single shot in modified test actions, were developed under this effort. The 7.92 mm combustible cartridge consisted essentially of a molded case with ribbed inner walls composed of ball propellant and a mixed cellulose ester (of acetic and butyric acids) binder. The 20 mm cartridge case was similar except that the inner wall of the case was smooth. These cases were loaded with the amount and type of loose granular propellant required to meet the desired ballistic performance. The primers used in these cartridges were also combustible. Since elimination of the metal cartridge case introduces the problem of obturation (sealing the chamber against loss of combustion gas), conventional small arms test actions were modified to obtain satisfactory obturation with the combustible rounds.

Tests were conducted in the United States with both the 7.92 mm and 20 mm combustible cartridges. The 7.92 mm round yielded low mean velocity (with individual shots exhibiting considerable velocity dispersion) as well as poor accuracy. In addition, the cartridge cases were not completely consumed, with propellant residue found in the test action after firing. The poor accuracy was attributed by SIDEM to notches cut into the bullet to secure proper adhesion between the projectile and the combustible cartridge case (3). The 20 mm combustible round (designed to be fired from a modified M24 test action and to duplicate the performance of the 20 mm M99 metal-cased round) was found to be generally unsatisfactory (4). At 70° F, the mean velocity obtained with the combustible round was approximately 120 ft/sec lower than that yielded by the standard M99 round. At temperatures other than 70° F (viz., 130°, 0°, -30°, and -65°F), 58 percent of the combustible rounds misfired. A considerable portion of the case was found to be unconsumed during the ballistic cycle. In addition, the combustible case was found to be very fragile, one round shattering after being dropped from a height of 30 inches. This development has since been terminated by the U. S. Air Force.

(2) SIDEM International, “Development of a Self-Consuming Cartridge,” Contract AF 61(514)-745C, Final Report, April 1957."


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Thanks Brian!


Fantastic cartridges! I have not seen the 25 - 30mm one in the middle before, would love to know more as well.
One question Tony, is there a primer on the 20x87? If so is it combustible like Brian mentioned of the German tests, or something else?


These are my notes on the 20 x 87:

This example was developed in the USA. The propellant was formed into a solid block with the shape of a bottlenecked cartridge case 87 mm long. Priming was electric using a pair of metal contacts. Overall length of the complete round is 158 mm and the weight is 175 g including an M99 TP projectile weighing 130 g.

One of the metal contacts can be seen at the base.

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Aha - found it - I think?!

This looks rather strange. Is the container that it’s in just for carrying and display?

20mm Hercules. Not what you are looking for, but related:

Historical Development Automatic Cannon Ammunition: 20 mm to 30 mm; Davis, 1984

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Thanks again, Brian.

I’m a bit frustrated as I have a memory of seeing an official ammo display board of caseless cannon rounds, including one like mine. It was possibly a couple of years ago and most likely on this forum… jog any memories?

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I’ve got these three, two of them last year at SLICS. No program info however. If I recall, there was a box of similar rounds at the Woodin Lab, which were terribly deteriorated and appeared to be molding.

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What is the caliber of these?

Would you have OAL and max. diameter for us?

Won’t be able to check them till maybe late this weekend, you may need to remind me. I’ve got training with two bomb squads, followed by a buying visit to an old collector and then the Ohio show. Priorities, sorry. I was able to dig up the above motioned photo from the Woodin Lab, however. I’ve left it full size to if desired folks can enlarge and look at the details. He had drawers full of the small caseless rounds in similar condition, plus plenty of nice ones. I note that all of these have a flat base.

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I had to click on the picture twice to get the full size.

No hurry at all!

Oh well, the image above is the best reason why everybody should document his valuable cartridges in a professional way (not with smart phones or “click-click” cams on the kitchen table).

This brings up a point, however. I don’t have a picture at work of the small caliber caseless in similar condition, but during discussion with Bill at the time he stated that he had no idea how to arrest the powder deterioration and preserver the rounds. Has anyone found a method, coating, treatment that can prevent this from occurring?

Thing is that the deterioration here is not the usual corrosion we know from metals or so as they are oxidizing on the surface.
The caseless stuff here has an inherent instability of chemical compounds (hard to foresee which of these will and which will not). Means if a composition has the ability or chemical instability to react with it’s own components, air or humidity little can be done in my (limited) view.
Maybe we have some chemists here who have some ideas on the issue.
As for now I would recommend to store all caseless cartridges inside a hermetically sealed container where oxygene is replaced by inert gas (CO2 ?) and which has a silica gel dryer inside. Then store in a cool place (fridge temperature) AND PRAY.

And before all that take those professional images, weights and detailed measurements.

Thank you!

It never ceases to amaze me how much experimental work has been done, and how poorly it was recorded at the time. Davis’s excellent publication is about the only source I know on US post-WW2 cannon ammo, and that covers only part of the period, for aircraft gun ammo.

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I’ve only got a small portion of the Davis document, do you know if it is available digitally?

I believe it is available via The IAA Research Center, online. Available to IAA members.

There is poor resolution copy on DTIC.

Is that the one where we request the special email/connection etc to get connected and have access? Still kinda waiting on that.

My understanding & I may well be wrong, is the slurry used to bond the powder (in smaller 5.56 mm U.S. caseless from this era) is the cause if the powder deteriation which inturn causes the green-crap bullet build-up.

I thought GIG Concepts (Lew Curtis) had a copy of Davis’s work available?