20mm Tround PGU-28 Projectile

This may seem too simple to collectors of U.S. medium-caliber cartridges. There are 20mm Tround cartridges made by Veritay, Inc. that used a PGU-28 projectile. These are seen in at least fired and unfired rounds, and in purpose-made dummies. Veritay put a little card inside the Trounds to identify the round and to promote the company, I assume. I have documented at least three different lot numbers of the live/fired rounds. Apparently, all of them, live and dummy, use a PGU-28 20mm TP bullet/projo.

Does anyone have a drawing/description of a “PGU-28” bullet/projo? I think they may be dirt common, but I’m not sure. I’d sure like to have a couple of them if they are not gold.

The two 20mm Trounds shown are at 50% to save screen space. The cartridges are 6.7 inches long and 1.6 inches across a flat side.



I have a fired case label below. hope it’s of help


Mel, I am not the one to finally answer but was the PGU-28 available in 1992 already?

The PGU series is the streamlined variant:

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Mel, as far as I know these trounds were tested using PGU-27 TP projectiles. The companion PGU-28 is a SAPHEI loading, not TP.

@EOD Alex, I don’t know the exact adoption date, but the procurement of the Raufoss PGU-28 round was solicited by the USAF as early as 1986.



For anyone else who missed it, these were loaded in 1992. (I just noticed the loading date on the Dummy round.) Thanks Mel and EOD.


From IAA Forum member Orpheus72’s website http://www.20mmcollector.net/ , a sectioned PGU28 projectile:

Versus a PGU27 projectile:

The PGU-28 took over from the M56 HEI as the standard ammo for the US M61A1/2 from the late 1980s, AFAIK. It was based on the Raufoss Multipurpose SAPHEI projectile (available in sizes from 12.7 to 40mm) which doesn’t have a conventional fuze, but an incendiary element in the tip which is ignited by a high-velocity impact. The streamlined shape gives it a longer effective range, so needs the fire control system to be modified for the different ballistics.

There are PGU-28A and PGU-28A/B variants, with minor alterations to the construction.

Things are starting to make sense now, thanks to all the replies. After I did the post I found a copy of a December 1992 Tround International Final Report on the 20mm Tround twin-barrel gun system. On page 31 it states: “The [20mm] Tround cartridge case accepts all types of [20mm] projectiles without modification. This includes both the M-50 series [?] 20mm, as well as the PGU 27/28, Phalanx projectiles, and the developmental APTS (Armor-Piercing Tubular Saboted) projectile by China Lake [Naval Ordnance Test Station], which allows a subcaliber penetrator to be fired from an aircraft.”

It makes sense that during testing, the preferred projectile would be the relatively inexpensive, inert PGU-27 and that test firing of the more expensive, complicated PGU-28 SAPHEI would be kept to a minimum. My dummy has a thin opaque plastic seal over the mouth, but I can see a blue projectile nose under it. Orpheus72’s web site and sectioned projectiles are great.

During one test, the gun achieved a rate of fire of 4,000 rounds per minute (67 rounds per second), or 2000 RPM from each fixed barrel; pretty quick for a 20mm.


Any chance of a copy of that report? I have no data on that gun.

Tony, All I have is a hard copy. I’ll see if I can scan/convert it to a PDF and ship you or anyone else a copy.

Thanks Mel, that would be great!

A bit of background information on the work by Tround International, a 1988 abstract on research & development proposal for Defense Small Business Innovation Research Program, U.S. Navy (DTIC Accession Number : ADA210042)

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Thanks. That’s a great explanation of why Dardick proposed to do the 20mm (plus the .50, 25mm, and 30mm), beyond the obvious of making money, by showing the advantage to the U.S. military of the Tround open-chamber system. Because it’s an unclassified public government document, I can quote it verbatim in the 20mm chapter of my book, which has grown a lot because of the replies to my post.

Brian, thanks for the lead!

It might be easier for most others here to give a direct link as many people will not know what to do with this reference: