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Why didn't proof testing work?

Hokkmike
OK, here is a question, and I remain a big SAKO fan, but with the recent past problems encountered by SAKO and bursting barrels I have a question. These rifles are all stamped with proof marks. Supposedly a proofed barrel is subject to a charge much greater than a typical cartridge load, right? Why then, did any problems with weakness in barrels not show up during these test? Isn't this exactly the kind of thing they are suppose to detect? Any ideas? Thanks!

Sako Fan
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2 comments

Date Votes
  • richbug
    It is possible that the proof loads themselves induced the stresses in the barrels that eventually led to their ruptures. Barrel can get unseen damage from proof loads.

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  • v35
    I view it as a "fatigue failure" which is really a misnomer.
    A small crack forming at a defect or or tool mark gets larger with each successive load until it finally lets go. You can see by examining the fracture, the conchoidal lines as the crack progressed through the material. Steel has the property called notch sensitivity which requires highly stressed parts to be very finely finished.
    In the USA, gun barrels and aircraft steel parts are not just 4130, 4140 or 8620 etc, steels have to be certified Gun Barrel Quality or Aircraft Quality and they come with test certificates from the steel mill.
    The SAE or AISI designation isn't good enough as evidenced by Sako Kabooms.
    There is plenty of steel out there with inclusions, seams,laps faulty welded tubing and other defects that will eventually fail at these defects.
    These Sako barrels (and Glock Kabooms)need to go not to the manufacturer but to a materials test lab for failure analysis.
    I believe it's rare that any American barrel made since WW2 will let go for almost any reason.
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