Posted by Kenshi on September 26, 2011 15:15:
quote:Kenshi I'm not doubting you word and I appreciate the info, but can you show me any data where it states a Spanish mauser or FR7 can't handle the pressure of a 762X51 or a 308W? If it was designed to handle 45k psi, it shouldn't go kaboom at 50k psi. That would be a mighty small window of safety. If I shoot mine it will be with 762X51 so I don't really see a problem.
First let me say that in my past life I was an Aerospace Structural and Weapons design engineer, and a Reliability and Maintainability engineer for the Lockheed Skunk Works in Palmdale Ca. Additionally I am an A&P Mechanic, a Master Machinist, a Certified Welder, and a Gunsmith with over 30 years of experience. I designed and tested "things", including weapons, for the F117, F22, F35, and "others". I am a Bladesmith and a Blacksmith.
In my job as a Reliability and Maintainability engineer I was tasked to test many items under increasing stress and pressure until they failed. I learned to recognize the failure modes, point of failure, and what the failure trends would be, at times by just examining something. Examining a somethings design criteria, material selection, the design itself, and the metallurgy to decide what the point of failure and point of catastrophic failure would be is what l did for a living, and I did that very well and it made me a better design engineer because of it.
When speaking or writing of failures, material failure and catastrophic material failure are two distinct and separate failure categories and modes.
I agree that something with a designed operating pressure of 45kpsi should safely handle a 50kpsi operating pressure and this was no doubt a factor in the re-barrel and chambering of the M93/FR7 to 7.62 NATO by the Spanish Military Engineers as that is within the common minimum IRL designed engineering safety factor of a 20% over build.
Without access to the Mauser design notes I would have to err on the side of caution and "assume" a 20% engineering design tolerance is what was actually used. I do not think that one would see a "Kaboom" (catastrophic) failure with a 5kpsi over pressure as that is approximately 11% of the design pressure. There would be an increase in overall stress however and recognizing the simple fact that all stress in accumulative, it would definitely increase to some degree the failures seen. Whether or not that is acceptable depends on the criteria they used to evaluate the design and design changes and I (without the design notes they used in the modification) can not obviously "speak" to that.
The issue of soft receiver locking lugs and the bolt to receiver issue is a different one and is dependent of the metallurgy and elasticity and recovery limits of the metal and the forces (bolt thrust) being applied.
Bolt thrust is dependent on a number of variables which include; cartridge taper, surface area of the cartridge base, case lubrication, case adherence, and instantaneous chamber pressures. Between two cartridges of equal taper, no lubrication or adherence changes, and equal case base area it is a simple mater of multiplying cartridge base surface area by chamber pressure to get a bolt thrust value between the two.
SOOOO based totally on the foregoing is it OK to re barrel, chamber and shoot 7.62 NATO Spec (7.62x51mm Mil Spec) in a M93 Mauser action in good material shape? I would say yes it is OK based on the foregoing discussion.
Any and all .308 Winchester loadings? HELL NO!! What is the pressure of the specific .308 Win loading one wants to use? In absence of data one MUST assume a 62kpsi value. To do otherwise is moronic and begs the answer of just what Darwin award is one trying to win for their family to display?
Because 7.62 NATO "looks" like .308 Winchester they ARE the same and are interchangeable? If anyone want to talk specific MIL SPEC vs SAAMI spec we can do that, there is A LOT more here than just a pressure difference.
It should be very easy to see why there is a bolt set back issue with the M93 Mauser action and the .308 Winchester cartridge.
An action designed for 45kpsi handling 50kpsi and the relatively minor increases in bolt thrust is one thing. Being designed for 45kpsi and handling 62kpsi and a major tonnage increase in bolt thrust is entirely something else. Is a catastrophic failure of the action also possible under these conditions? Depending on the health of the action YES. Maybe not today, maybe not tomorrow, but next week? Being a firm believer in Murphys Laws of engineering, it is just a roll of the dice away at these levels of stress.