Wes Janson wrote:
What is this 20mm Marquardt, and how did it work? I can't find anything about it online anywhere
This could actually be covered in two or three separate threads, but here's the quick answer. I can do no better than the beautifully succint prose of George Chinn, so here's a quote from "The Machine Gun", Vol III pg. 165:
"After the end of hostilities with Germany in 1945, the Navy Department sent Frank R. Marquardt, a naval technician, to Europe to investigate German aircraft machine gun development. After reviewing the status of the German revolver gun development, Marquardt became interested in the possibilities of obtaining high firing rates with low weight by use of a rotating chamber. He felt that the single barrel, five chamber, revolver guns under development were unneccessarily compromised to make use of conventional recoil absorbing, gas operating, and mechanical ramming mechanisms as a result of the German anxiety to meet an urgent requirement."
These revolver guns were, of course, the Mauser MG-213 and derivatives. To quote Chinn again (Vol III pg. 47):
"The German gas-operated gun MG-213, upon which the development of all models of the revolver-type of automatic cannon developed by the United States was based, is a gas-operated, belt-fed, electrically fired, pneumatically charged weapon which fires at a rate of approximately 1,200 rounds per minute. By changing certain parts, it may be converted from a 20mm to 30-mm weapon;..."
The US M39[A1] Revolver cannon (which everybody and their dog worked on at one point or another) was a direct descendent of the MG-213. Chambered in 20mm Vulcan, it managed only about 750 rpm. But it had the advantage of minimal "spin-up" time, due to its lower rotational inertia comapred to multi-barrelled Gatling guns.
SO, Marquardt came up with an extremely advanced design to counter the known problems with conventional revolver cannon.
1) He used two barrels to effectively double the rate of fire.
2) One barrel started the firing burst, and the other ended it, leaving the first barrel with a round chambered ready to start firing again.
3) In the middle of a burst, both barrels essentially fire simultaneously.
4) The barrels fire out-of-battery, to keep the reciprocating parts floating instead of being hammered back-and forth in recoil and counter-recoil.
5) He used an eight-chambered cylinder, with at all times two chamber positions empty and available for through-cooling if required.
6) Instead of abrubtly starting and stopping the cylinder rotation to index it, he used the cylinder's rotation to store recoil energy like a flywheel, and then recovered the cylinder's roatational energy in order to operate the gun - thereby slowing the cylinder gradually.
7) In the first version constructed, Marquardt used "projectors" to *fire* the ammo (complete loaded rounds) into the chamber, rather than waiting for a mechanical reciprocating mechanism to load it. The projectors were essentially sleeves that held the 20mm rounds. The projectors, which were linked into a belt, each had an electric 20mm cartridge primer in the base. The primer launched the 20mm round forward into the appropriate cylinder chamber. Ramming forces were so intense that in some tests, the *neck* of the cartridges were fully engraved by the rifling!
8) The projectiles were initially designed with a conical flange. The flange helped seal the cylinder gap (as did an obturating sleeve). The flange also helped prevent projos from being pulled out of their casings by momentum as the round slammed home in the chamber. Finally, in early designs the projos were spun up by a short length of rifling, and then the flange was swaged down by the smooth bore to reduce the projos' aerodynamic drag.
9) Marquardt used a pneumatic accumulator to store energy not only to charge the gun, but also for buffering and ejecting. A clever system self-regulated the ejection force of empty casings and dud rounds.
10) The gun was mainly made out of aluminum. Prototypes were made out of titanium.
11) The rates of fire of the adopted versions were about 4000+ rpm, much higher than the rates of simpler revolver cannon. Short bursts were fired in some tests at over 5100 rpm. Not bad for only two barrels!
The Marquardt was adopted by the US Navy as the Mk 11 Gun. Mod 0 used a unique (brass!) case with no extractor groove or rim (smooth bottom!). Later versions became more conventional, and used the 20mm "Navy" Mk 100 series ammo (when it became clear that this ammo was going to be mass-produced for the Mk 12 Hispano guns).
The Marquardt was only fielded in an external gun pod. As a buddy of mine said, "there wasn't anybody smart enough to work on the gun!".
Ammo and projector cups are very rare today (I paid $400 recently for a projector to go with the $400 single round of early Marquardt ammo in my collection).
Skunk Ape wrote:
Especially FIFTYGUY. Wow.
Thanks!
Actually, "Steel vs. Brass" is a hot topic among us cannon shooters. There are plenty of anecdotes supporting once side or another. Sometimes you don't have much choice as to what kind of casings you can scrounge up, and sometimes it's hard to find any casings at all! As a result, we're intensely concerned with what types are OK to shoot, and how many times they can be reused. I personally like to keep my pretty brass casings for display, and shoot up the grungy steel casings instead.
