HPT and MPI testing. Why?

[GTF425]

Neat.

[GTF425]

Our 5.56 (E3) bolts are pretty different than anything else out there in the 5.56 world. Rounded lugs for reduced stress risers in the bolt, reduced cam pin hole for a stronger web, repositioned extractor pivot position for better mechanical advantage on the extractor, and more reinforcement on the lugs beside the extractor. 20k bolt life on short barrel suppressed guns (yeah, springs still need to be changed at their normal intervals).

The SR-25 and the MWS bolt carriers were very similar, but then both took diverging but similar paths. The lug dimensions are close enough to at least be nominally cross-compatible. LMT does good stuff, I hold Carl and his crew in high regard.

You have a representative of KAC publicly endorsing a 20k round life with the bolts. It's a lifecycle that the company advertises and employees are on record endorsing.

It's not in their blanket warranty policy, but it is aggressively marketed as a key feature and is recycled in the industry as fact with their products.

So you're correct with the published warranty, and users who repeat the official statements of KAC employees are correct in assuming said public statements are made with a significant data pool of end users to support it.

[lysander]

Well, a 2007 test showed a standard M4 bolt has over a 15,000 mean rounds to replacement, during the test twenty M4 fired 36,000 rounds each and consumed 46 bolts. All of them needed at least one bolt, but some did go over 20,000 rounds.

[NoVA5326]

Sounds like a gov study.. mean #'s are so wide ranging as to be essentially useless.

The far left side of the bell curve, first failures, would be more useful for preemptive replacement on an in-service weapon if one intended to substantially derisk having an operational failure.

Perhaps left of the modal (vs mean) if one wanted to save money on a parts replacement matrix for a schoolhouse weapon.. if willing to accept the downtime.

In a schoolhouse using m4a1w/ greentip, no F/A & no suppressors, 1st visually perceptible cracks would appear ~ 7500rds

Likely the #'s have shifted left with m855a1 being introduced.

A systemic answer would be to have a bolt that outlast the barrel, and to rigorously enforce discarding the bolt with mated barrel (when shot out). This would prevent unknown life bolts being circulated through your n.

[lysander]

Sounds like a gov study.. mean #'s are so wide ranging as to be essentially useless.

The far left side of the bell curve, first failures, would be more useful for preemptive replacement on an in-service weapon if one intended to substantially derisk having an operational failure. [1]

Perhaps left of the modal (vs mean) if one wanted to save money on a parts replacement matrix for a schoolhouse weapon.. if willing to accept the downtime.

In a schoolhouse using m4a1w/ greentip, no F/A & no suppressors, 1st visually perceptible cracks would appear ~ 7500rds [2]

Likely the #'s have shifted left with m855a1 being introduced. [3]

A systemic answer would be to have a bolt that outlast the barrel, and to rigorously enforce discarding the bolt with mated barrel (when shot out). This would prevent unknown life bolts being circulated through your n.[4]

1) The first failure was about 10,500, the next 15,00 or so, the most were in the 17,500 to 20,500 range, a few further out.

2) Is that from some study, your experience, or someone else's experience? And, what time frame?

3) The test was repeated in 2015, just to see if M855A1 changed things. Answer not really, but that report does not have near the raw data of the earlier one, so you can't calculate other things, you might want to.

4) That is basically what they do with the M4s.

In any case, I fail to see any evidence of HPT harming the bolts to any extent.

[MegademiC]

1) The first failure was about 10,500, the next 15,00 or so, the most were in the 17,500 to 20,500 range, a few further out.

2) Is that from some study, your experience, or someone else's experience? And, what time frame?

3) The test was repeated in 2015, just to see if M855A1 changed things. Answer not really, but that report does not have near the raw data of the earlier one, so you can't calculate other things, you might want to.

4) That is basically what they do with the M4s.

In any case, I fail to see any evidence of HPT harming the bolts to any extent.

To the underlined, that makes sense. As you stated, if you dont exceed the yield point, the effects would not be measurable - within the effects of all the other variables.

Which brings up a point, people want to fine tune minutia within a system that incorporates multiple variables, its not realistic without a single, dedicated test system, or massive identical case subjects under controlled circumstances

[lysander]

To the underlined, that makes sense. As you stated, if you dont exceed the yield point, the effects would not be measurable - within the effects of all the other variables.

Which brings up a point, people want to fine tune minutia within a system that incorporates multiple variables, its not realistic without a single, dedicated test system, or massive identical case subjects under controlled circumstances

Or, have a reasonably good mathematical model of the system, which for the gas system isn't that hard to do, one is available.

J. H. Spurk, "The Gas Flow in Gas Operated Weapons," Ballistic Research Laboratories Report No. 1475, February 1970

Nathan Gerber, "Sensitivity Study of Rifle Gas Systems," Ballistic Research Laboratories Report No. 1524, January 1971

W. M. Werner, "Comparison of a Theoretical and Experimental Study of the Gas System in the M16A1 Rifle," Ballistic Research Laboratory Report No. 1548, August 1971

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The thing that amuses me to no end are the people that insist that you have to stick to the MIL-Spec on minutia like the cadmium plated detents for the takedown and pivot pins, and then go on about how great their chrome-silicon springs are . . .

[the AR-15 Junkie]

That 3rd link is excellent, especially what it says on page 39.

[frankmissing]

You have a representative of KAC publicly endorsing a 20k round life with the bolts. It's a lifecycle that the company advertises and employees are on record endorsing.

It's not in their blanket warranty policy, but it is aggressively marketed as a key feature and is recycled in the industry as fact with their products.

So you're correct with the published warranty, and users who repeat the official statements of KAC employees are correct in assuming said public statements are made with a significant data pool of end users to support it.

I usually trust recommendations, but what is written in the guarantee is not always a fact!!

[prepare]

That 3rd link is excellent, especially what it says on page 39.

Wonder what the conclusion would be of a similar test done today with the current M4?