First off - MPI without HPT is pretty pointless.

If a parts is stressed (HPT), the weak areas will open up and become visible to some form of penetrant inspection. If the parts is never stressed the weal areas will never become visible.

Second, the point stressing the parts is some stuff is just not visible from the outside, (see Figure 1).

And third, the idea that a single 120% stress test will some how hurt the part is laughable. That's not how that works. Steel has a fatigue limit, if the stresses are below this limit, it will not fail due to fatigue. Small arms barrels live in this range. M16/AR bolts are subject to low cycle fatigue. This means the stresses in the bolt under normal operation exceed the yield strength in some areas, and eventually cracks will develop. Measured life expectancy of bolts (military bolts) has shown the first crack can show up as early as 5,000 rounds, and some bolts will last over 20,000 rounds. That one loading that was 20% higher than the average is not going to shift that huge uncertainty zone enough to be noticeable.

(If you honesty believe that an HPT will shorten the life of the part, don't ever go to your doctor for a medical stress test.)

. . . they also warrant their bolts for +20,000 rounds . . .
Please, provide a link to this. I have heard this over and over but their website states something completely different.


Figure 1