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I was fooling around in my shop today and made an experimental adjustable gas valve for my MAS 49/56. I'll try to explain. I machined a threadless bolt to replace the pin on the grenade shut off valve. Instead of having the slot on the pin on the inside to provide a track for the gas to get to the gas tube I drilled two correct size holes 90 degrees from one another. Then I threaded the end that protrudes from block (the side that the little C-clip is on to hold it from falling out. Next I drilled a hole through the body of this replacement I made on the opposite end of the C-clip end. I threaded it and then made a screw to fit it. This screw will act like a valve and completely close off those two holes from passing any gas to one another. I put it in my MAS and bolted it tight and ran the adjustment screw all the ways in. I just loaded one round in the magazine, charged the rifle, and fired it. As I thought it didn't function the action at all because I had the gas all the way off. Next I repeated the test just opening the adjustment screw a little at a time until I got full functioning and the bolt locked back on an empty magazine.

Now I call it this an experimental test adjustable gas system because I removed the original grenade gas cut-off lever and pin. I believe I can make a pin, with the adjustable screw, that would replace the original pin. What this means is that your MAS will have the grenade shut off lever and it will work just like the original, but when it's in the firing position to fire ammo from the rifle it will be adjustable. It would hardly be a noticeable change from the original.

What do any of you think?

Joe
 

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Can you post photos of the new parts?
 

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Discussion Starter #4
Here's a picture of the MAS 49/56 grenade shut off lever, the original piston pin that slides through the gas block, and my second prototype adjustable piston pin. My pin is almost finish as all I have to do is cut it to length, shape the end that goes through the half moon hole in the grenade shut off lever, and cut the little C-Clip retaining slot. You can see the allen head socket screw that is the gas adjuster. I'll replace my first prototype with this one and my MAS will appear as normal.



Joe
 

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That is pretty cool. I seem to remember some shop came up with an adjustable gas valve for the 7.62 NATO converted guns so as to reduce the number of ripped off case heads. I was never able to discover the details of how it works.

I have one question about your design. What stops the Allen screw from backing out/rotating in?
 

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Hi Joe! I am very interested in your design! Although I am not a metalworker and don't completely understand how you made it, I used to have a Hakim and know how a gas valve works. What would be the advantage to an adjustible gas valve in the 49/56? Would it be to fire various types of 7.5, or could it go as far as a .308? And if so, any other modifications necessary? I would think cutting the recoil spring (as Century did) would no longer be necessary. Anything else come to mind?

Thank you!!! Dave
 

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Discussion Starter #7
What stops the allen screw from moving is friction. You can also put Blue Loc-Tite on it.

The advantage is for the 308 conversion because I feel the 308 is much hotter and harder on the action then the 7.5. Century made a big mistake cutting a few coils off the recoil spring when they converted to 308. 308 is hotter then 7.5 so why would they do that?

I've been shooting my rifle since the conversion and it's really nice now. Instead of ejecting the brass into the next county it throws it much closer and the rifle functions flawlessly.

Joe
 

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Many Years ago.....someone was trying this type of gas adjustment......

So many years ago......I don't remember how it worked.....but I did keep the Photo

Joe your approach appears much more simple and less noticable...... Nice.

Buddy


 

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Discussion Starter #12
Many Years ago.....someone was trying this type of gas adjustment......

So many years ago......I don't remember how it worked.....but I did keep the Photo

Joe your approach appears much more simple and less noticable...... Nice.

Buddy


Thanks for your kind words. Exactly, I didn't want to alter the rifle. I can just switch back to the original piston valve. I was out shooting my rifle yesterday. For the first time it piled the empties into one neat little spot and I didn't lose one piece of brass. I noticed that ejection is consistent now, whereas before it threw the brass every which way.

Joe
 

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Would that be the only modification necessary then to switch from 7.5 to .308? Seems the harsh recoil with ripped rims is the major problem?

Dave
 

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Discussion Starter #14
Would that be the only modification necessary then to switch from 7.5 to .308? Seems the harsh recoil with ripped rims is the major problem?

Dave
The harsh recoil would only rip through the rim if the chamber is rough and the case sticks to it, or the case is still obturated to the chamber walls for whatever reason.

Joe
 

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ya know, I am glad I didn't post what I had been working on, I took a small threaded screw longer than the length of the valve hole, then two nuts, I dremelled a slot for full on gas pressure, then to reduce gas pressure I lossen two nuts and move the screw forward or backward closing off the gas slot I cut in the screw, making the gas pressure less, then tighten the nuts against the gas block on each side, didn't get a chance to test it yet, but bad ugly and one has to keep the slotted head of the bolt/screw straight up and down and be careful, tested with compressed air, seemed to do "something", but not with charisma that has.

Remember, I accidently/unknowingly destroyed a mas 49-56 .308 conversion I didn't realize was only working cause I had oily cartridges until the day I didn't have but nice commercial thin brass reloads that I shot previously but weren't oily this time(bad rough chamber problem, double slam fire, then bulged barrel of ripped up brass down the bore followed by a slam fire projectile, previously mentioned ), my former other one that a friend is thankful for the various small parts and a receiver he has "plans" for, and the my other one I have had trouble with, I wished I still had access to machine tools, I could really see where this could be done rather easily, like a long time ago, nice work.
 

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Discussion Starter #16
ya know, I am glad I didn't post what I had been working on, I took a small threaded screw longer than the length of the valve hole, then two nuts, I dremelled a slot for full on gas pressure, then to reduce gas pressure I lossen two nuts and move the screw forward or backward closing off the gas slot I cut in the screw, making the gas pressure less, then tighten the nuts against the gas block on each side, didn't get a chance to test it yet, but bad ugly and one has to keep the slotted head of the bolt/screw straight up and down and be careful, tested with compressed air, seemed to do "something", but not with charisma that has.

Remember, I accidently/unknowingly destroyed a mas 49-56 .308 conversion I didn't realize was only working cause I had oily cartridges until the day I didn't have but nice commercial thin brass reloads that I shot previously but weren't oily this time(bad rough chamber problem, double slam fire, then bulged barrel of ripped up brass down the bore followed by a slam fire projectile, previously mentioned ), my former other one that a friend is thankful for the various small parts and a receiver he has "plans" for, and the my other one I have had trouble with, I wished I still had access to machine tools, I could really see where this could be done rather easily, like a long time ago, nice work.
I'm glad that nothing but you ego and rifle were hurt. The one can be fixed, the other replaced. Becareful what you do. Being I use commercial primers the first thing I did was modify the firing pin and put a spring on it to prevent an inertia firing. Seems to be working well.

Joe
 

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Gathering together the various comments I have seen about the 308 MAS 49/56 conversions, I have come up with the following list.

1) The chamber machining was often rough. This contributes to case sticking and ripped off case haeds.

2) Century removed some coils from the recoil spring. I can only surmise that this was done to reduce the chances of slam fires on soft primered commercial 308 ammo.

3) Century decided that the higher pressure of 308 over 7.5x54 was no big deal. WRONG! From memory, 308 is about a 52k CUP cartridge, and 7.5x54 is nearer 40k CUP. That is a BIG difference. With the rough chambers and an excess of gas, case head separations are bound to occur.

Given all this, it is clear that a reduced or adjustable gas system is a must along with a thorough chamber deburring exercise.
 

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Discussion Starter #18
Gathering together the various comments I have seen about the 308 MAS 49/56 conversions, I have come up with the following list.

1) The chamber machining was often rough. This contributes to case sticking and ripped off case haeds.

2) Century removed some coils from the recoil spring. I can only surmise that this was done to reduce the chances of slam fires on soft primered commercial 308 ammo.

3) Century decided that the higher pressure of 308 over 7.5x54 was no big deal. WRONG! From memory, 308 is about a 52k CUP cartridge, and 7.5x54 is nearer 40k CUP. That is a BIG difference. With the rough chambers and an excess of gas, case head separations are bound to occur.

Given all this, it is clear that a reduced or adjustable gas system is a must along with a thorough chamber deburring exercise.
Kelt will disagree with us on the 308 running at a higher pressure then the 7.5 French. I'm not talking a few pounds I'm talking a major difference. Other then that I totally agree with you. My rifle with my three mods is just perfect now.

Joe
 
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