Fired 20x110 Oerlikon "S"


#1

Hi,
I don’t collect artillery or heavy machinegun ammo but I’ve found this case into a ruined house and I would like to know what is it because I haven’t got any information about this kind of cartridges at home.According to me this case has been shawn down.However according to me it is certainly english made.
Rim diam. .877"
Base diam. .988"
Case lenght 4.26"


#2

This is a 20x110 Oerlikon “S” shell case, made By Bridgeport Brass Co., Bridgeport, Conneticut, USA in 1942.

This was used in the 20mm Oerlikon AA gun, fitted to British and American ships during WW2 and after (I think into the late 1980s/early 1990s for the UK.), and possibly even still today for some countries’ warships.

The neck appears odd because this weapon fired before the round was fully forward in the chamber so the neck blew out. This was called “advanced primer ignition”. I’m sure someone else can give you more information on the gun. Here is a photo of one from Wikipeida on the Australian WW2 Minesweeper HMAS Castlemaine.


#3

Thanks Falcon.So it isn’t english nor shawn down…sorry but I am familiar only with 20 mm Flak 38, 50 Browning & soviet and 14,5 X 115 soviet.

Pivi


#4
  • @ Pivi: Your 20X110RB Oerlikon “S” brass shell case was not shortened. There is a difference between the unfired and the fired 20X110RB shell case [brass or steel], the fired one has a deformed neck which is very normal. The “Mk.-II” mark shows “a brass case with British type primer”. The letter “B” inside of a diamond [ ] and “1942” show only the US company which manufactured the 20X110RB brass shell case and the year. Black ink markings stamped on the side of the 20X110RB brass shell case give more information about the type of propellant used, type [code] of projectile, the facility which loaded the round and the date of loading. After so many years most of the 20X110RB shell cases don’t have left those black ink markings. —> NOTE: Other possible headstamp markings on the US made 20X110RB rounds: “Mk.I” [Brass case with original primer], “Mk.II” or “Mk.2” [see above], “Mk.III” or “Mk.3” [Steel case] and “Mk.IV” or “Mk.4” [Brass case with reinforced primer]. Liviu 12/21/07

#5

Falcon

I must admit that I have never heard of “advanced primer ignition”. What is it and where can I read about it?

Ray


#6

Hey Falcon

Here’s a link that explains it fairly well: usstexasbb35.com/20mm_gun.htm

I MEANT: Hey Ray


#7

Hey Falcon, errrr, I mean Rick,

Well that’s embarrasing! That was probably on the Gunners Mate tests. I’m sure i got the answer right. I just couldn’t remember it. :) :)

Still, I understand the blowback principal. But I find it hard to believe that the case would be extracted while the pressure was still high enough to expand the shoulder and neck without rupturing the head. The whole concept of blowback is that the primer ignites the charge while the bolt or breech is still travelling forward and the pressure is low enough before the mechanism can recover from the forward momentum and start back.

But, I’m probably wrong. Again

ray


#8

Sorry, but what is the meaning of the “S” letter in the name of this cartridge?
As I wrote above I know very little about heavy caliber ammo

Pivi


#9

Rick

Aha! Maybe I’m not as dumb as I look. I went thru some old references that i have and one of them describes the spring loaded, greased cartridge, mechanism as a “Blow Forward”. So I’ll bet that my GM test worded it that way and I aced it. That’s my story, for now.

Ray


#10

[quote=“Pivi”]Sorry, but what is the meaning of the “S” letter in the name of this cartridge?
As I wrote above I know very little about heavy caliber ammo

Pivi[/quote]
“S” Is simply the designator for the model of the cannon. There is the earlier Oerlikon Type L, and the later FF, FFS and FFL versions, designed for aircraft use. I am unaware of the actual meaning of the letters.

Tony Williams has a very good article on the history and development of the Oerlikon (see link below):

http://www.quarry.nildram.co.uk/apib.html[/url]


#11

A friend of mine was in the process of restoring, to firing condition, a demilled 20MM Oerlikon. Quite a project, but very doable with enough money. He’s has a Class 2 FFL, so all is legit. Anyway, as there are no relaodable hulls available AND a pretty much zero, civilian, supply of new brass, his efforts went into rebating(machining) the base of “normal” hulls. He purchased a 55 gal. drum of TP projectiles. Been a while since I spoke with him, but I’m guessing little progress was made or else I would have heard about it. On a side note, the gun mount pictured above weighs about 700 lbs. Very thick casting. Helped load one up in a pickup at Knob Creek a few years back. Vendors at Knob Creek also have a huge selection of larger caliber stuff for collecting.
All that to say, a very interesting gun and cartridge. Wish I had one in my collection.
Knob Creek is a shooting range in north central Kentucky, noted for their Spring and Fall machinegun shooting fests. An unbelievable event.


#12

Rick, apparently some people form 20mm oerlikon brass from 20x102 Vulcan brass. That must be an awful lot of work, and not something I would have thought possible due to the Vulcan’s much larger base diameter at where the case walls mee the head. It must take alot of lathe work, and one hell of a powerful press.


#13

I never witnessed the hull conversion, but undertood the process. Yes, the base was machined and dies were manufactured for a hydraulic press. The primer pocket needed converting as well. My friend is well versed in all things machining. AND, he has lots of expendable income.


#14

The gun sounds like it would be good fun to fire tracer through at night when it is finished. I would like to go to the Knob Creek shoot at some time.


#15

ANYTHING is fun to fire tracers through!


#16

I tried firing a WW2 Kynoch .303 G Mark II tracer round through a Lee Enfield and it didnt light up. (Surprisingly there are no restrictions on tracer in the UK). I think it was a combination of the round being 66 years old and not having enough range (about 40 yards before a chalk face). I expected it not to be far enough, I would have sooner pulled it and kept it as an inert but had no puller then. For anyone who may be interested I still have the case, it is headstamped “K1941 GII” and had a CN bullet.


#17
  • @ Pivi: There were a few types of 20mm Oerlikon rounds: 20mm Oerlikon “F” [short] / 20X71RB, 20mm Oerlikon “L” / 20X100RB, 20mm Oerlikon “S” / 20X110RB and others. Those letters represent series according with the type of the gun. —> NOTE: Many of the WW2 made 20mm Oerlikon “S” [20X110RB] fired brass shell cases do have hairline cracks just above the extractor groove. I know this because I try to avoid those 20X110RB cracked fired brass shell cases for my collection. Liviu 12/21/07

#18

[quote=“Ray Meketa”]Hey Falcon, errrr, I mean Rick,

Well that’s embarrasing! That was probably on the Gunners Mate tests. I’m sure i got the answer right. I just couldn’t remember it. :) :)

Still, I understand the blowback principal. But I find it hard to believe that the case would be extracted while the pressure was still high enough to expand the shoulder and neck without rupturing the head. The whole concept of blowback is that the primer ignites the charge while the bolt or breech is still travelling forward and the pressure is low enough before the mechanism can recover from the forward momentum and start back.

But, I’m probably wrong. Again

ray[/quote]

Ray,

The one important thing that the link to the explaination of the operation of this gun missed out is that the chamber is much longer than the cartridge case. If you slip a loose cartridge into the chamber is disappears out of sight. The rebated rim allows the bolthead to follow the cartridge into the chamber. This was discussed in some detail in an earlier thread, I likened the case to a greased piston.

gravelbelly


#19

20x102? While it’s a common enough casing, the 20x110 Hispano Suzza case would be a heck of a lot less work to convert Base measurement is only a few thou smaller, and the shoulder is only a couple thou larger, vs the .10+ larger for both measurements on the x102 case. In either case you would have to bush the primer hole to convert it so something more readily available.


#20

Ray, the Oerlikon API blowback 20mm guns used cartridges designed with a rebated rim so that the bolt can slide into an extended chamber despite the extractor being hooked around the rim. Because the cartridge is fired while it is still moving forwards, the chamber is not shaped to fit the cartridge at the instant of firing. The necked-down region of the case is therefore unsupported and is easily blown out on firing. The fired case of course extracts itself by blowback pressure, and by the time it is clear of the chamber the pressure has indeed had time to drop.