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Metal Fatigue Question for Experts

Discussion in 'Shooting Related Threads' started by drgondog, Apr 12, 2013.

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  1. drgondog

    drgondog Member

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    Fatigue in a shotgun is far less likely than say, a helicopter blade or any airframe parts experiencing harmonic and reversible loads. From an airframe design standpoint you use far lower allowable stress factors to improve the fatigue life than you would for conventional propulsion system.

    For example, the wings on an F-105 are getting nearly 30,000 hours before major repairs/replacement due to stress/fatigue failures

    Loads on a shotgun due to firing are neither harmonic nor reversible per se. More common is the wear and tear on hinge pins, top levers, action blocks, peening of firing pins, etc
     
  2. bevolt

    bevolt Member

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    similar question... For semi-autos, is there a rule of thumb method to judge wear on the receiver where the barrel slides in? For example, there is always a bit of play between the barrel and the receiver when the barrel is inserted. How can one differentiate between wear from repeated use and manufacturing tolerance? How much wear is too much?
     
  3. SlowArrow

    SlowArrow Member

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    Not claiming to be an expert - but I am an engineer with too many years building and supporting steel products that go are supposed to go boom. If you are just talking fatigue, it is all about the stress/strain curve - how highly stressed is the part. If you properly design it with low enough stresses for the selected material, you will have infinite fatigue life. That doesn't mean the parts won't wear out, or suffer some other failure mode (stress corrosion comes to mind),fatigue just isn't one of them.

    There are other types of issues like fracture toughness with the steels that can cause problems, but most of these have nothing to do with round count. There are so many different failure modes that could result in a failure, you almost have to look to a really good materials analysis group to assess what type of failure you are looking at. For any modern fIrearm, I wouldn't worry about fatigue - you will wear the thing out long before a part fails in fatigue. Improper heat treatment or hardening, material flaws, and most often customer modifications are a much larger concern - but even then the risks are super low. I just don't see shotguns as being a highly loaded or stressed item.
     
  4. OLD ONE EYE

    OLD ONE EYE Well-Known Member

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    BEVOLT I am no expert but shot a lot of automatics over the years the first thing I look at are the rails inside the receiver and the back of the receiver for hammering from the bolt. Then look at the barrel lock up area where the bolt locks into the barrel if badly worn it will show hammered or rounded off in the barrel area. I will also say that I have seen this area welded up and recut and used again. If in doubt have a gunsmith, look at it for a few dollars money well spent on any used gun you are not sure of the history of.
    Buddy
     
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