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  #1  
Old 09-19-2019, 11:01 AM
JLaughlin JLaughlin is offline
 
Join Date: Aug 2018
Location: Maryland
Posts: 14
Default S marked gas cylinder lock screw

My first CMP M1 came with this gas cylinder lock screw. As you can see in the photos the only marking is what is left of an "S".

https://flic.kr/p/2hhH2Uz
https://flic.kr/p/2hhKGxG
https://flic.kr/p/2hhH5kr

It does not return to the closed position on its own after being opened. When it is closed manually it does remain shut with a perceptible click into a detent inside.

When installed in the rifle, the functioning is normal. After comparing its function to a SA "P" "Triangle" marked poppet gas cylinder lock screw, I thought that the spring inside the "S" marked screw might have been broken. In my research I came across a thread here that included the following link: http://www.m1garand.net/Data_Files/gasscrew.pdf

It looks like the first gas cylinder lock screw designed for grenade launchers (replacing the single slot screw) was the B147851 "S". This gas cylinder lock screw was used in 1943 before being replaced with the poppet type gas cylinder lock screw that was spring loaded to return to the closed position.

Am I correct in identifying my "S" marked gas cylinder lock screw as a B147851 "S"? The article says that upon removal of the grenade launcher, this screw was designed to remain open until closed by the firing of the following cartridge.

Last edited by JLaughlin; 09-19-2019 at 06:11 PM.
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  #2  
Old 09-19-2019, 11:24 AM
Rock Rock is online now
 
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Quote:
Originally Posted by JLaughlin View Post
The article says that upon removal of the grenade launcher, this screw was designed to remain open until closed by the firing of the following cartridge.
The open poppet allowed dirt to enter the gas cylinder. To eliminate the dirt problem, the spring was added to keep it closed.
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  #3  
Old 09-19-2019, 12:29 PM
Det. Jason 714 Det. Jason 714 is offline
 
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I've never heard one remaining open until the second round was fired. That would mean the top round would of been a grenade launching cartridge followed by a ball round in the en bloc. Would be too easy to flip around in the heat of combat and send a FMJ into the grenade being launched. I would just DX the one you have unless you are launching lots of grenades.
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Old 09-19-2019, 12:40 PM
JLaughlin JLaughlin is offline
 
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Quote:
Originally Posted by Det. Jason 714 View Post
I've never heard one remaining open until the second round was fired. That would mean the top round would of been a grenade launching cartridge followed by a ball round in the en bloc. Would be too easy to flip around in the heat of combat and send a FMJ into the grenade being launched. I would just DX the one you have unless you are launching lots of grenades.
I don't have a grenade launcher...yet
But it seems like it would work in theory. The launcher would hold the screw open until removed and the rifle would have to be operated manually like a straight pull bolt the same as it would with the spring loaded gas screw.

I'm not sure how grenadiers would have stored their ammo but I would think that they would keep the grenade launching cartridges in separate en-blocs than their ball cartridges.
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  #5  
Old 09-19-2019, 12:48 PM
Det. Jason 714 Det. Jason 714 is offline
 
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A definite must have. This package is the best deal around.

https://www.gunpartscorp.com/products/546750
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Old 09-19-2019, 12:52 PM
JLaughlin JLaughlin is offline
 
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Quote:
Originally Posted by Det. Jason 714 View Post
A definite must have. This package is the best deal around.

https://www.gunpartscorp.com/products/546750
Yes! I've been looking at that one for a while actually. How is it?
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  #7  
Old 09-19-2019, 01:35 PM
Det. Jason 714 Det. Jason 714 is offline
 
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Default Very fun

Quote:
Originally Posted by JLaughlin View Post
Yes! I've been looking at that one for a while actually. How is it?
I've only used blanks with it, haven't pulled the trigger on grenade launcher rounds.
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  #8  
Old 09-19-2019, 02:38 PM
Orlando Orlando is offline
 
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I hate to call anything rare but those type gas screws you don't see everyday. In all the years I have been messing with garands I have one run across one.A lot of guys never will see one
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  #9  
Old 09-19-2019, 03:24 PM
Ronwall Ronwall is online now
 
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The S looks hand stamped. If I'm not mistaken it was made by SA only in 1943. It's a cool piece for sure.
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Old 09-19-2019, 03:33 PM
Nodak71 Nodak71 is offline
 
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I thought these were fairly rare, picked up a few many years ago. No idea where the other collector found them. Don't think I have seen any others.
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