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 Author  Topic: How does a 20mm Oerlikon function?
  David Waples

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of David Waples  Posted on: Sep 25, 2009 - 9:23pm
I'm trying to understand how an Oerlikon functions. I've seen photos of the gun with the spring cover and slides forward covering most of the barrel and others with the slide back and spring compressed and most of the barrel exposed. Can somebody maybe explain the following...

1) When loading the gun is the slide in the rear position or extended?
2) When a shot has been fired what is the idle position of the slide. Is it forward covering most of the barrel or is it to the rear with the springs compressed?

Thanks so much for your help with this question.
Dave

David Waples

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Jeff D

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jeff D   Send Email To Jeff D Posted on: Sep 26, 2009 - 2:59am
Hi David, this should answer your questions ad nauseum:

http://www.hnsa.org/doc/gun20mm/index.htm



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David Waples

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of David Waples  Posted on: Sep 26, 2009 - 7:46am
That's perfect. It explains why I see the breech bar/spring casing in different positions and how they get to be that way. It's also going to help me with some details for the gun. There's a lot of detail that I need to try and pick out for my models.

I would love to hear from the vets as to what condition they kept this gun while at base. For example were they always cocked and ready to go or was it more common to relax the barrels springs when not in use. It looks like a touch gun to cock!

Thanks so much
Dave

David Waples

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Jeff D

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jeff D   Send Email To Jeff D Posted on: Sep 27, 2009 - 4:32am
Happy to help David, the 20mm is a unique gun and I was glad they put the manual up. Hard to get the details right from a bunch of fuzzy photos eh? Reworking my drawing is on my to-do list...

They also have the Mark 4 mount manual up which you've probably noticed.



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David Waples

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of David Waples  Posted on: Sep 28, 2009 - 4:46am
I hadn't noticed the 40mm before. I need to spend some more time looking over this site. Thanks for pointing it out!
Dave

David Waples

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BobPic

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Sep 29, 2009 - 11:26am
Let me take a crack at this. Our skipper insisted we all know how to act as gunner on all weapons, so I had a few turns, but don't remember much. The gun was never left in the cocked position. It was tough to cock, in fact a couple of our smaller guys couldn't master it. The gun was always pointed skyward and there was a small cable to hold it in that position. To cock the gun, another cable was hooked on the upper edge of the spring assembly and the other end was hooked to a cleat somewhere on the base. The gunner grabbed the handles and jerked the gun down to the horizontal position, which tightened the cable and pulled the spring back. If there was a cartridge that misfired, you had to recock the gun. After a round fired, the recoil recocked the gun and it fired automatically. It was a great gun and kept the loaders very busy.


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Will Day

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Will Day   Send Email To Will Day Posted on: Sep 29, 2009 - 2:01pm
Bobpic: Do you remember if there were traverse stops on the bow guns to keep them from accidentely hitting the boat during combat?

Will

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David Waples

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of David Waples  Posted on: Sep 29, 2009 - 7:48pm
Hi Bob,
Thanks so much for that information. I'm enjoying learning more about these guns and how they operated on the boats. I picked up on the cocking method that you described. Many of the photos I have show the gun elevated as you describe with the breach bar and spring cover fully after towards the gunner. I assumed this was a gun that has been cocked and ready to receive a magazine or to be fired. Am I wrong about that?

Regarding the cable used to cock the gun. I've seen this on the pedistol type mounts seen on the 103 class Elco's. Was this true of other types of mounts as well? What kind did your boat have?

Thanks again and I look forward to hearing from you.
Dave

David Waples

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BobPic

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Sep 30, 2009 - 6:18am
On our boat there were no restrictions on pointing the 20mm. There were numerous recounts about how close the gunner came to hitting the radar or other part of the boat. I did see a few boats that had rigged constraints of one sort or other but it never caught on in our squadron. Gunners were often cautioned about shooting across the deck. Our exec usually served as fire control and watched for this. Wasn't a good deal but I don't remember any accident report due to this.


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BobPic

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Sep 30, 2009 - 6:31am
The 20mm's were usually cocked whenever there was a threat that they might be needed. That included in-port air raid alerts. On patrol we usually cocked the guns as we neared the area where we expected combat. Similarly, the magazines were prepared by winding up the spring. One bit of trivia that sticks in my mind was the apparent "looseness" of the barrel spring. As the gun fired, the spring did not follow one compression per round, but rattled loosely between rounds.
The cocking cable on our pedestal mounted guns hooked low on the pedestal. It was tight when the gun was upright but it was routed around a metal protrusion such that as the muzzle was lowered it tightened the cable and pulled back the very strong barrel spring. I didn't pay much attention to gunmounts on other boats and do not know if they differed.


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