French MAS 49/56 (7.62mm NATO)

[gunnut]

Morning Gunnut,

I have been digging through boxes from a past life, found some notes and found the following undated entry:

"Moderate burning powders for port pressure problems in medium capacity cases: faster than IMR 4320 and slower than IMR 3031".

Under that, I wrote "Handloader" #148, pg. 28. I imagine I was referring to "Handloader" magazine.

IIRC, I was loading around "bolt over base" malfunctions in an AG42 that were suspected to be related to peak port pressure.

In the burning rate range listed above, I know that I settled on IMR 4895 for the 6.5 x 55 Swedish Mauser round.

If you do "roll your own" to get around your problem, that burning rate range I provided does include several ball propellants and as I previously stated, I am not enamored with that configuration as a solution to the problem at hand.

Hope this helps!

William

How does burn rate affect chamber and port pressure? How do I know if a certain propellant is fast burning or slow burning?

What is this "bolt over base" problem you encountered?

I'm not trying to achieve world class accuracy with any of my reloads. I just want to have some inexpensive plinking at the same time have a working rifle. :))

Thanks for all your help.

[gunnut]

Just found this for you.

CUP Versus PSI

Tony

That is facinating. I always wondered how the chamber pressure was measured. Now we have strain gauge that can measure the force exerted on a piece of metal. People back then came up with some very smart ideas to solve interesting mechanical problems.

[Swift Sword]

How does burn rate affect chamber and port pressure? How do I know if a certain propellant is fast burning or slow burning?

G.N.,

1. Regarding burn rate, think of your weapon's barrel kind of like a cylinder in a piston engine: the barrel is the cylinder, the cartridge case is a gasket sealing one end, the bullet is the piston and the muzzle is the eventual exhaust port.

When the powder ignites in it's confined space, it rapidly burns to form high pressure gas. Said gas drives piston down cylinder and pressure levels lower as volume increases until pressure drops to the point where the action can be opened safely (i.e. when the exhaust port opens or in this case when the bullet clears the muzzle).

In a gas operated weapon such as yours, gas is tapped out of a port a distance from the chamber that is calculated to allow for a high enough pressure to start the operating cycle yet close enough to the muzzle that the pressure in the bore drops to a level that is safe for the action to open.

If you use powder that burns too fast, you start to have certain problems because that fast burning powder in the firing chamber builds up pressure very quickly to high levels. Things that can happen include blown case heads and primers (i.e. you blew the gasket), burst chamber walls and other phenomenon such as stuck cases (in manually operated repeaters), etc.

If you use a powder that burns too slow, you suffer other issues such as spewing a lot of extra goo out the muzzle in terms of smoke, flash blast, etc in manually operated weapons with attendant losses in efficiency and uniformity of performance.

In your gas operated weapon, a powder that is too slow burning will drive up the pressure further down the barrel near the gas port in which case the pressure at the port will be outside of the design specifications and things begin to go wrong.

A powder that is too fast for your application might spike chamber pressure but as cylinder volume increases with bullet travel, you are left in a position of not having correct pressure at the gas port which could lead to various malfunctions as well, perhaps failures to eject or short stroke related feed issues.

Does this help put things in perspective? This explanation is a bit cursory and I hope someone with a greater deal of experience can shed more light on it if I got it wrong or was too vague.

2. A powder burning rate chart is a fairly common thing. Google something like "cannister powder burning rate chart" or a similar query and that should put you right on it. CAVEAT: most of these charts are relative burning rate and not a scientific scale.

There will also be a burning rate chart in any reloading manual. As a shooter and gun guy in general, you should get a manual anyway even if you do not pursue loading in a big way. The reloading manual has cartridge dimensions, historical details, charts for computing trajectories and other very useful information to the journeyman and more advanced shooter.

What is this "bolt over base" problem you encountered?

Names for failures, stoppages and malfunctions can vary from time to place so I will just describe it: a situation where the weapon is left out of battery with the bolt having slipped past the cartridge head with the cartridge lodged in the feed way. Causes can include extractor failing to engage on the feed stroke, magazine spring weakness, bolt velocity and one or two other gremlins.

In gas operated weapons, especially direct impingement weapons, my experience with bolt over base problems has lead me to zero in on bolt velocity first which brings us around to port pressure.

I'm not trying to achieve world class accuracy with any of my reloads. I just want to have some inexpensive plinking at the same time have a working rifle. :))

Your accuracy will almost no doubt increase. You will have finer control over powder density, charge weight, case length, cartridge overall length and some other variables in small lots than the Big Guys do in their large runs.

In general, can get exceptional accuracy with your control over bullet seating depth if you load to a length that puts the bullet closer to the lands. However, because you have a self loading weapon, you will want to use a projectile with a cannellure which will ultimately limit your seating depth options.

Thanks for all your help.

No problem!

Hope you have a good weekend.

William

[24RIMA]

I don't have any problem with my MAS 49/56 so far.
This is an excellent semi-auto rifle if you know how to use it in combat.
However, I prefer the M14 Scout myself.

[gunnut]

I don't have any problem with my MAS 49/56 so far.
This is an excellent semi-auto rifle if you know how to use it in combat.
However, I prefer the M14 Scout myself.

I agree with you sir. It is a most rugged and robust combat rifle. Do you have yours in the original 7.5mm French or converted 7.62mm NATO?

[24RIMA]

To be honest with you , I have two.
One as the MAS 49/56 converted in 308, the second as MAS 49 in 7.5 only. The second one was use in the Indochina conflict the most , where the 49/56 was carried in the field of Algeria War to early 1982.
I did my training with the MAS.
I prefer the AR10 now,much lighter !!
:)


Did you say that you had an ejection problem,
I might know why...please describe again.

[24RIMA]

Yes, I have a French rifle.

This rifle does have a gas cut-off for launching rifle grenades. It's activated by flipping up the rear rifle grenade sight.

------------------------------------------------
My question is if it's ok to partially close the gas cut-off by flippin up the sight half way? It's a mechanical device, not digital. So theoretically I can close it paritially by flipping up the sight partially. Is that how adjustible gas piston on other rifles work? Or do I have to hand load some rounds with 2/3 the charge of a standard 7.62mm NATO?

----------------------------------------------------
You got it !
This problem is known from the MAS 49/56.
The French Paratroopers were using some kind of rubber around the flipping part
before jumping. I suggest that you use some black 10 inches plastic cable Ties around it to keep the flipping down at all time. You will find them at Homedepot.
Good luck !


PS : The flipping part was open when a grenade was installed on the top of the barrel.

[Guest]

Mas

I have a converted MAS to 7.62. When I first got it, I loved it, true, it is ugly, BUT it is a semiauto 7.62 farrrrrrr cheaper than a M14. I bought 500 rounds of surplus ammo. When I went to the range and fired it, I noticed...
HIGH pressure in the form of flattened primers. So I did my home work and
found the difference in the original MAs loads and .308 loads. It scared me.
I did not shoot it for over a year seeing how I didnt want to blow my head off. What I did was pulled all the bullets out, measured the power in it, and cut it back to 12% of the original charge. It worked great!!! No more flattened primers. Now I am pulling the reainder bullets, replacing it with 125 grain ballist tips, and using 37.5 grains of H4895. I am going to work up the load now but still stay in the safe zone. I never had any problems with cycling
even with the full power rounds. I sent off for scope mounts for the MAS, so I plan on using the gun deer hunting. I also in the future will move up to 150 grain bullets, will let you know how that goes.

[24RIMA]

Yes it's ok to flipdown the gaz cut off but like you just said, the 308 pressure is to strong for this riffle. It's like asking a 5 years to swallow a 325 mg aspirin pill..
This riffle was design for French Paratrooper regiments during the Algeria conflict, the old 49 was to long and too heavy for "le travail de ratissage" in the djebel....
However most of those men prefered the MAT 49 instead.

[24RIMA]

The M1A1 Carabine was very much appreciated as well in Algeria by the French Paratrooper..

[OSOK]

I've owned two MAS self loaders - a 49 and a 49/56 - both chambered for the 7.5 Mas and unmolested. They worked and shot great. Sold them both off though...

I would suggest going to Parallax Bill's C&R forums. This is the first gun board that I ever joined and was at one time the French Rifle forum moderator. Go there and do a search for this and you will find the answers that you seek. ;)

[gunnut]

Parallax Bill's...got it. Thanks.

[OSOK]

NP here you go: French & Italian Rifle Forum - General Gun Collecting - ParallaxBill's Curio & Relic and Military Surplus Firearms Forums - Message Board - Yuku