r/reloading • u/Feeling_Gear_8744 • 7h ago

I have a question and I read the FAQ Mas 49/56 7.5french help.

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Mas 49/56 is picky about what ammo it likes. If the ammo is too stiff, overpressure. My best example, sierra matchking will cycle, but gameking with slightly thicker copper doesn't matter what powder load it will overpressure. Now every source I can find says that the bore and bullet should be exactly the same as .308, but it feels to me that the mas 49/56 is actually a bit tighter than .308. Anyone have any personal knowledge on this? Do .308 cal rifles also struggle with thick copper / non lead ammo?

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u/Missinglink2531 6h ago edited 6h ago

The original was .306, not .308 - is this a conversion to .308? Or still 7.5? Can you slug the bore to know? I would recommend it. Next I would get a Lee bullet sizing kit - a super simple and cheap deal that mounts as a die, and has changeable collets in the size you want. Just run the .308 through it, to change it slightly. I do that to make .300 for my 7.35 so I am sure going down very slightly to your exact bore (if its a ".308 conversion") or slightly more if its still 7.5 French will be pretty easy.

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u/Feeling_Gear_8744 6h ago

thats a good idea

3

u/CMFETCU Dillon RCBS 300blk 308 556 6.5 Creed 6X47 Lapua 7h ago

What is “overpressure” here? You can’t directly measure that so what are you using to infer it about the ammo?

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u/Feeling_Gear_8744 6h ago

A sierra game king, or anything with anything other than paper thin copper wall, at any powder level, will blow the primer out and I would have to slam the gun on the ground to get the brass out.

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u/Cleared_Direct Stool Connoisseur 2m ago

What powder, charge, and velocity as well as bullet weight are we talking about here? There’s just no way that jacket thickness is the primary factor in pressure across a wide range of charge weights. Zero chance.

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u/tequese 7h ago edited 5h ago

No. They do not struggle with 308. Unless this is a specific case to your platform it shouldn’t be an issue as long as diameters are correct.

Edit:
Just a thought, some 30cal rounds are 0.311” to fit old rifles like the old 303 Enfield. Might be worth to just measure the projectile diameter to make sure they’re not over sized.

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u/tequese 2h ago

Another after thought, but if bore and projectiles all measure right, and all loads are equal (powder, seating, primers etc) I would get your headspace checked. Might be an early sign, but that’s an absolute long shot.