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Thread: Bolt life question.

  1. #141
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    Quote Originally Posted by dangertree View Post
    I have not experienced extraction issues on well running carbines with Mk262.
    This was during the development of the load. The high pressure of the carbine gas system combined with a live round that sat in a 200-300 degree chamber during a lull in shooting would cause some extraction issues.

    They (blackhills) had to work the load around the limits of the carbine gas system.
    "You people have too much time on your hands." - scottryan

  2. #142
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    I'm dying to know what SF unit issued a BM...
    We miss you, AC.
    We miss you, ToddG.

  3. #143
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    Quote Originally Posted by Magic_Salad0892 View Post
    I'm dying to know what SF unit issued a BM...
    It could only be the SEAL team six cause they get the best.
    Quote Originally Posted by C4IGrant View Post
    Colt builds War Horses, not show ponies.
    Quote Originally Posted by Iraqgunz View Post
    This is 2012. The world is going to end this December and people are still trying to debate the merits of piece of shit, cost cutting crap AR's. Really?

  4. #144
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    Quote Originally Posted by dangertree View Post
    because I do know people who have used Stag Arms rifles in combat.
    Emphasis mine, can we all PLEASE stop mistaking this as a valid pivot-point on which to hinge an assertion meant to be anything other than anecdotal?

    It matches my own personal assertion that there hasn't ever been a produced-in-numbers lefty AR from any vendor that hasn't been a soup sandwich....

    ...in that each (conflicting) assertion is functionally worthless without something besides a desire to be "right" to support it without documentation. We all know people; that's not unique, nor is knowing people that have used stuff in combat in the last decade or so.

    Let's move it back to talking about bolt life considerations, per the thread's title, and not yet another "less-filling/tastes-great" mess regarding whole guns and their respective roll-marks.
    Contractor scum, AAV

  5. #145
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    Quote Originally Posted by skullworks View Post
    Please note that there is a difference between pushing the bolt forward so that is has NO contact with the BE lugs and pushing it forward so it has LESS pressure during contact with the BE lugs. What I am saying is that the DI system pushes the bolt forward so that it has LESS pressure on the lugs during contact than when rotated in a piston system. Therefore less stress is incurred on the bolt and BE lugs in a DI system than in a piston system, whereby the bolt life should be longer in a DI system (from a purely mechanical standpoint).
    The only way the pressure inside the carrier can push the bolt forward any appreciable degree is if the pressure wave enters the carrier after the pressure in the bore has dropped to near atmospheric
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

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  6. #146
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    Rogers and Caputo stated on LF that TDP bolts rarely fail at the cam pin. Normally they shed the lugs next to the extractor and the failure is discovered during maintenance.

    The goal should be a 20,000 round barrel and bolt life. Replace both at once.

  7. #147
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    Quote Originally Posted by RyanB View Post
    Rogers and Caputo stated on LF that TDP bolts rarely fail at the cam pin. Normally they shed the lugs next to the extractor and the failure is discovered during maintenance.

    The goal should be a 20,000 round barrel and bolt life. Replace both at once.
    20k rounds for a USGI milspec bolt? Where do you get this info?
    Ken Bloxton
    Skill > Gear

  8. #148
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    The goal for the PIP, not current life expectancy.

  9. #149
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    Quote Originally Posted by RyanB View Post
    The goal for the PIP, not current life expectancy.
    SOCOM was replacing bolts at 6,000 in 2006 with harsh firing schedules. This was before they broke so they could have maybe gone another 2,000. They also noted you can ge 10,000 out of a bolt used under normal schedules, so if a FF rail increases bolt life and they get one made of different materials i can see 10,000+ on harsh schedules and 20,000 under normal ones.
    Last edited by sinlessorrow; 08-21-12 at 14:21.
    Quote Originally Posted by C4IGrant View Post
    Colt builds War Horses, not show ponies.
    Quote Originally Posted by Iraqgunz View Post
    This is 2012. The world is going to end this December and people are still trying to debate the merits of piece of shit, cost cutting crap AR's. Really?

  10. #150
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    Quote Originally Posted by RyanB View Post
    Normally they shed the lugs next to the extractor and the failure is discovered during maintenance.
    Yep... here's the conclusions from a report I saw some place...

    Failure Analysis of the M16 Rifle Bolt
    V.Y. Yu*, J.G. Kohl, R.A. Crapanzano, M.W. Davies, A.G. Elam, M.K. Veach
    Department of Civil and Mechanical Engineering
    United States Military Academy
    West Point, NY 10996, USA


    4. Conclusions
    The fracture of the M16 bolt resulted from a cumulative effect of high stress concentrations at the fillet radius and the additional stress concentration imposed by the presence of localized pitting at the surface. The bolt possesses many fillet regions which impose numerous areas of high stress concentration. In particular, two fillets experienced higher stress immediately adjacent to the round extractor due to the non-contiguous feature of the bolt. These two specific areas of high stress concentration also corresponded to the same location where failure of the bolt occurred in all fractured bolt specimens. Micrographs obtained from the scanning electron microscope of the fractured surface showed localized pitting at the failure initiation site. In addition, transgranular crack propagation near the pit formations in the fillet regions was observed. The localized pits formed near the locking lugs also served as high stress concentration points. The presence of pits in the material amplified the stresses of the bolt in the locking lug region which already had a high stress concentration due to the irregular geometry of the bolt. This cumulative stress concentration provides a good indicator why the crack initiated and propagated from this region.

    The wear observed in the controlled experiment indicates the mechanism of why the corrosion pits formed near the locking lug fillet by exposing the Carpenter Steel 158 base metal to the environment. Vickers microhardness readings near the fillet region show that the bolt was not uniformly case hardened. Comparison of the microhardness readings near the fillet region and 10 mm from this region show a disparity of approximately 100 units. The softer, less carburized region near the fillet contributes to the formation of a wear area after firing just 1800 rounds.

    5. Acknowledgements
    The authors would like to thank Mr. Victor K. Champagne, Jr. and the Materials Analysis Group at the Army Research Laboratory in Aberdeen Proving Grounds, MD for helpful discussions and for performing SEM work.

    6. References

    [1] Three-dimensional Pro-Engineer® model of M16 bolt from U.S. Army Testing and Armament Command, Rock Island, IL.

    [2] Individual Weapon Systems & 3-D Technical Data Development Team, U.S. Army Testing and Armament Command, Rock Island, IL.

    [3] Alloy data Carpenter No. 158® Alloy, Carpenter Technology Corporation, 1981.
    Last edited by markm; 08-21-12 at 14:28.
    "You people have too much time on your hands." - scottryan

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