7.5 what to do about excessive chamber?
I got a nice, new, unissued MAS 1936. It shoots very well.
The chamber is oversize and bulges the cases to about 0.487 at a point about 0.3 from the back of the round. Unfired Grafs brass measures .475 at that point and my Lee die returns the brass to that dimension.
I am concerned about expanding and resizing the case just ahead of the case head. If it work hardens I could have a head separation.
I can't just neck size. The cases won't go far enough in the die to size just the neck without the bulge in the body (at 0.3 from the back of the round) being forced back down to original size.
The bottom half of the case is so hard to anneal without softening the case head. Necks crack from firing and resizing, but you can anneal a neck.
So, do I just ignore it? Is a case head separation safely contained by the MAS 36?
If not, would it be safe to use with neck sizing only? I would try and find a neck sizer or maybe a resizing die for a 30 cal round with a larger body which would allow my oversize, fired cases to be neck sized, without resizing the bulged part 0.3" ahead of the back of the case.
BTW, I found some information from Vectan which said the round's normal working pressure was 3300bar or 47,000 psi. Balle C, which was the rifle's normal ammo, ran at around 40,000psi but the MAS 36 was supposed to also use Balle D and other types which used higher pressure.
The chamber is oversize and bulges the cases to about 0.487 at a point about 0.3 from the back of the round. Unfired Grafs brass measures .475 at that point and my Lee die returns the brass to that dimension.
I am concerned about expanding and resizing the case just ahead of the case head. If it work hardens I could have a head separation.
I can't just neck size. The cases won't go far enough in the die to size just the neck without the bulge in the body (at 0.3 from the back of the round) being forced back down to original size.
The bottom half of the case is so hard to anneal without softening the case head. Necks crack from firing and resizing, but you can anneal a neck.
So, do I just ignore it? Is a case head separation safely contained by the MAS 36?
If not, would it be safe to use with neck sizing only? I would try and find a neck sizer or maybe a resizing die for a 30 cal round with a larger body which would allow my oversize, fired cases to be neck sized, without resizing the bulged part 0.3" ahead of the back of the case.
BTW, I found some information from Vectan which said the round's normal working pressure was 3300bar or 47,000 psi. Balle C, which was the rifle's normal ammo, ran at around 40,000psi but the MAS 36 was supposed to also use Balle D and other types which used higher pressure.
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The chamber was cut oversize, and for best results you need to have a custom die made.
Short of that, find a neck sizing die for something like a 308 Win (or build a holder for a Wilson/redding type neck sizing bushing and decap with a universal decapper).
BTW, 1 BAR is 1 ATMOS is 14.7psi, so 3300BAR is closer to 48,500psi0 -
Military rifles are manufactured with reliability of function as the primary objective. Reloading fired brass was a unknown concept for the French.
With the amount of head expansion that you have found with your fired brass. The only way you could safely have multiple reloads is have RCBS make a custom full length resizing die. To my way of thinking if you want to do much shooting with the rifle with you reloads, this would be the only feasible if expensive way to do it safely.0 -
I was also considering rechambering to 7.5x55 Swiss because the case is slightly larger in all dimensions, and is still a bit bigger than my oversize chamber. 0 -
Might be a good idea.
You might use a combination of FL die and neck sizer and just run the
case partially into the FL die sufficient to chamber in your rifle.
Alternatively, you can send a few fired cases to RCBS to get a custom FL die and maybe open up your seater.
I like the idea of a proper chamber and 7.5 would do it BUT you may lose
some reliability in feeding.
Don't forget to remark the barrel if you rechamber.
The French Foreign Legion and some sandy African colonies may account for loose chambering.
The concept that someday the MAS may have collector's value is very speculative.
It's your rifle so do what you will to enjoy it now.0 -
Soreshoulder,
I would hold off on re-chambering to 7.5x55 Swiss. The case has enough different dimensions so that feeding may be an issue. Also, if collectablility of this rifle goes up then it will be original and not in another chamber, which would hurt the value.
I would call Redding and tell them your problem. I did with my 7.5x55 K-31 and found they already had the right die. Seems the K-31 was cut with a roomier chamber than previous Swiss rifles. They all used the same ammo though. Maybe dirty chambers were a problem before? I know several military gun makers whose chambers are a tad larger than the ammo dimensions. If they have to make a special die it's not so cost prohibitive. I know when I called RCBS about my Swiss they wanted an exorbitant amount.0 -
This is a common problem in Japanese WWII weapons. This was no mistake, the Japanese military found that having over-sized chambers aided in shell exaction. BUT as a civilian owner/shooter it's a pain! One trick we use is a piece of 1/4" masking tape, rapped just above the exaction groove all the way around (but NOT overlapped!). This helps center the cartridge in the chamber and when fired the swelling is now spread all around the shell case and not jut to one side. This was you'll be able to reload afew times more. Good Luck! 0 -
Lee will make you a custom neck sizer pretty reasonably. 0
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