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Spindle Valve Closed

This is a discussion on Spindle Valve Closed within the The M14 forums, part of the M14 M1A Forum category; I have a question about shooting the M1A with the gas cylinder spindle valve closed. A friend of mine closed his and tried to shoot ...


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Old June 5th, 2012, 04:50 PM   #1
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Spindle Valve Closed

I have a question about shooting the M1A with the gas cylinder spindle valve closed.

A friend of mine closed his and tried to shoot the rifle as a straight pull bolt action to see if there was any noticeable difference in accuracy.

When he closed the valve and fired, he couldnt easily extract the fired casing.

Whats the cause of this and how can he fire the rifle, spindle valve closed without the case being hard to extract?

Thanks for the help.

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Old June 5th, 2012, 05:00 PM   #2
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The case expands when fired. Closing the spindle valve results in slightly more dwell in the chamber pressure which probably keeps the case from shrinking back as much as it would with the more rapid drop in pressure with the valve open. This would cause the brass to stick in the chamber.

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Last edited by Ted Brown; June 5th, 2012 at 05:33 PM.
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Old June 5th, 2012, 05:12 PM   #3
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To add to what Ted was saying. When the round is fired normally the bolt unlocks, and rotates while moving slightly to the rear, then the bolt goes all the way back to the rear and completes extraction. When it does this twisting and pulling motion together it prevents the case from more or less seating itself against the chamber walls. I would assume that since he is preventing this from happening, the case is fully expanded against the chamber wall, not in a manner like it was designed to do. Thats just IMO. I could be wrong.

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Old June 5th, 2012, 05:16 PM   #4
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Spotlessly clean helps also.

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Old June 5th, 2012, 05:36 PM   #5
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Quote:
Originally Posted by AsaSpades View Post
To add to what Ted was saying. When the round is fired normally the bolt unlocks, and rotates while moving slightly to the rear, then the bolt goes all the way back to the rear and completes extraction. When it does this twisting and pulling motion together it prevents the case from more or less seating itself against the chamber walls. I would assume that since he is preventing this from happening, the case is fully expanded against the chamber wall, not in a manner like it was designed to do. Thats just IMO. I could be wrong.

Agreed. This is easily seen in easily adjustable gas systems (like my FAL's)--not enough gas causes the rounds to get a bit sticky...

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Old June 5th, 2012, 05:40 PM   #6
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The leverage of the system is working against you as well. There's different geometry than with a bolt rifle.

I was "demonstrating" something to a friend with a clip full of fired unsized brass with my Garand once. I only demonstrated that I was a dope since it froze up the action and I needed a rubber mallet on the oprod to get the case back out again.

-J.

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Old June 5th, 2012, 05:44 PM   #7
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Originally Posted by jroosa View Post
The leverage of the system is working against you as well. There's different geometry than with a bolt rifle.

I was "demonstrating" something to a friend with a clip full of fired unsized brass with my Garand once. I only demonstrated that I was a dope since it froze up the action and I needed a rubber mallet on the oprod to get the case back out again.

-J.
Great first post. Doesn't work for a function check, either.

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Old June 5th, 2012, 06:05 PM   #8
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Barrel?

What barrel? Is it chrome lined? Headspace? What brass, commercial or USGI?
Ammo type?

Jim

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Old June 5th, 2012, 06:56 PM   #9
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This is well known occurence and I've never read a well stated explanation as to why it happens but as others have said, the case has swollen to a large enough size that it is actually slightly larger than the chamber in one dimension or another, the case becomes swaged in to the chamber space.

Don't forget that the chamber pressure actually expands the chamber itself to some degree. If the chamber pressure is increased (due to back pressure caused by the valve being turned off?) then both the case and the chamber will expand more than they would otherwise. The increase in pressure could be just enough to not exceed the yield point of the chamber steel (allowing the chamber to return to it's original dimensions) while exceeding the yield strength of the brass case (causing the case to remain larger than it's original size).

So, while the steel of the chamber returns to it's original size and shape, the brass case doesn't. The brass case would be longer and/or larger in diameter than it was originally. That means that it would be larger than the chamber and it would stick.

The amount of headspace and the condition of the receiver could have an impact on this problem too. If the headspace dimension of the case were very close to the headspace dimension of the chamber, then it would be easier for the case to stick (I needed to correct my original statement and remove the part where I said "take less of an increase in pressure for the case to stick"). If the receiver were worn more than normal, then it might be possible for the bolt to be pushed back more than normal while under max pressure. The case would stretch to a longer length and then when the pressure drops the bolt would return to it's original position but the case would now be longer than normal and it would tend to stick in the chamber.

I do know that when I fire my brass with the valve turned off, I have no problems with extracting the cases. I also know that I haven't noticed any major improvement in my group sizes when I turn off the gas. At least nothing consistently better that would cause me to use this technique as a way to improve my groups.

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Old June 5th, 2012, 08:12 PM   #10
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I totally agree with what these guys are saying, but another reason it may be happening to go along with their replies is the ammo you were using. I too have closed my spindle and depending on what ammo I was shooting, I sometimes had the same result as you did, sometimes not.

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Old June 6th, 2012, 04:39 AM   #11
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I had a feeling it had to do with everything you guys listed in your posts. I'll direct him this way to read this thread.

Again thanks for the help fellas

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