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Thread: a stronger AR-bolt-is it possible?

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    Gunco Addicted for life j427x's Avatar
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    Default a stronger AR-bolt-is it possible?

    during my last tour of that dirty-dusty sand-flea infested unmentionable place. i did witness a couple of m4 bolts that failed. now even the mention of this fact will get you banned from some of the mall ninja sites. i don't know if this was some kind of QC issue with that batch of m4's or just the general abuse and bad conditions adding up to the bolts breaking the lugs off in the field.

    i sort of think the cause was very long periods of sustained full automatic firing, being too dry and getting some of that flour like sand in the barrel extension--but that is just my theory.

    anyway with the advent of 6.8spc, the 6.5grendel and the return of the 7.62x39 to the ar-15 type of platform. there has been a increase in bolt failures. nothing drastic--some will pretend it could blow the bolt any second. but enough for concern as the little 5.56 bolt has been streached far beyond its origional design.

    the 6.5 looks to be the best candidate for a failure--with the bolt really opened up and AA's bolts have the additional "feature" of having the bolt face recessed an extra .010?? mine hasent broke yet. and i don't think it will any time soon no more than i fire it. but i wouldn't want to trust my life in the sand pit to such a thin bolt and i am thinking if you really put the rounds through it- that bolt is a likely suspect for a failure. even if it is made of kryptonite!!

    7.62x39 bolts are about the same--but generally arn't cut as deep. you see on the internet more 7.62x39 bolts that have failed. some think these failed bolts came from china--but i suspect that the 7.62x39 bolts fail because 7.62x39 is still cheap compared to 6.5/6.8 and there for get a lot more use and abuse.

    OK now we have settled the WHY-- lets look for a solution.

    if you wanted to put a hot round in an AR type rifle-- could there be a way to strengthen the bolt without increasing its size too much? the idea is to get as much as you can without going to a bigger platform like the AR-10

    i have often thought a six-lug bolt with slightly larger and thicker lugs "might" solve the problem. you would have to have a coustom "headspace" and re work the barrel extension for such an attempt.

    or maybe just lugs that are a bit longer--and reach back further on the bolt maybe??


    then the limit would be the barrel extension. but i have never seen a BE fail?

    any thoughts on the ar bolt??

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    gunco irregular moleman's Avatar
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    I think it was stoner or someone working with the stoner 63 rifle that came up with making the lugs on either side of the extractor a little thicker to compensate for the missing lug where the extractor is in the ar15 type bolt. I don't think you could change the bolt design much without also changing the bolt carrier which controls how much the bolt rotates. It would seem to me that if you went to a fewer number of larger lugs then you would also have to change how much the bolt needs to rotate in order to turn into and out of battery. I also think a bolt with 5-6 bigger lugs would strengthen the design and might also help it run better when its dirty.

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    Gunco Veteran [486]'s Avatar
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    If you have a round with a smaller diameter case head you'll have less bolt thrust, though you can't really make a longer case fit in the AR...

    Maybe try lapping your bolt lugs to the barrel extension, that would reduce the amount the bolt flexes in use, and increase it's life. You just gotta find a bolt that headspaces tight...

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    Gunco Addicted for life j427x's Avatar
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    Default some broken 7.62x39 bolts

    notice the broken bolts broke at the same place.

    one wonders if this weapon has some kind of out of spec barrel extension?

    would an reinforcement of that one broken lug shore the 7.62x39 bolts up?

    on my latest 7.62x39 CAR i did cut down the lug opposite the extractor by 2/3ds height. sort of like the LMT bolt. this bolt is a model 1 sales bolt.
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    No Hope For Me 1biggun's Avatar
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    well according to remington there new super duper wonder round for the AR15 the 30 RAR or what ever they want to call it uses a special bolt that is stronger some sort of a customied AR 10 bolt.

    Remington Introduces new 30 Remington AR Cartridge AccurateShooter.com Bulletin

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    JBobby jroberts1968's Avatar
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    The bottom line is the AR in itself is a week design and that is why we are the only country to adopt this system. I have several and enjoy shooting them but lets face fact there are better wheels out there. If the bureaucrats in DC and the DOD ever got there moral compass in the correct direction our troops would be equipped with the best. Now that the F22 is scrapped maybe our guys can get up armoe and some cleaning kits. Sorry Just spoke to a couple of friends from the sandbox and I am sending them cleaning supplies and replacement parts.
    Remember when we was playing matchbox cars in science class? Who's retarded now?

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    Gunco Addicted for life j427x's Avatar
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    Default looks like a ar-10/ar-15 hybred

    Quote Originally Posted by 1biggun View Post
    well according to remington there new super duper wonder round for the AR15 the 30 RAR or what ever they want to call it uses a special bolt that is stronger some sort of a customied AR 10 bolt.

    Remington Introduces new 30 Remington AR Cartridge AccurateShooter.com Bulletin

    looks like they mated the ar-10 type upper bolt/barrel extension to an AR-15 type lower. would certainly be stronger--at the expense of weight ans size.

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    No Hope For Me 1biggun's Avatar
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    yea the extension is slightly biggger as is the bolt. I doubt the weight increase would be much. remington gives a weight of there gun it could be compared to a AR with the same profile barrel to get a general idea of the increase.

    The bottom line is the AR in itself is a week design and that is why we are the only country to adopt this system.

    WRONG
    lots of countries over 80 that have used the m16.
    M16 rifle - Wikipedia, the free encyclopedia

    Imoo the bolt streanth of the AR is the least of the guns design problems. Id be more concerned about the jamming when dirty and other operation issues.

    while not as strong as the AK bolt the AR is not really that bad. if you compare some issues other arms have had thoughout history.

    It may be me, but seems that most bolt failures are in commercial AR15 that are possably not up to the specs they should be. there is also issues from non 5.56 nato ammo and calibur that the bolt was never intended for. Im no expert here on AR,s/M16,s
    and the above pics show more pics of broken bolts than i have even heard of failing in a AK so obviously there not perfect.

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    gunco irregular moleman's Avatar
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    I can see how the 762x39 bolts would be more prone to cracking at the bolt lugs. The ring that encompasses the case head is much thinner. Once a crack started there it could continue until the lug failed. All of my ar15 bolts are the 5.56 size and so far I haven't had any issues with cracking. I wonder if those broken bolts were out of a car length gas system since they open at a slightly higher pressure than the 20" length?

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    Gunco Addicted for life j427x's Avatar
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    i have seen m-16's with 50,000+ rounds on the bolts with no bolt failures and carbines/M4s with 10,000+ of 5.56. the strength of a good bolt in 5.56 is not a question.

    the life of the bolts is pretty darned good--considering no defects or bad steel when they are made. lots of nations use the m-16 series and lots of military weapons besides the m-16 uses the same or at least very similar type of bolt.

    what this discussion is about is the larger cut bolts for the 7.62x39/6.5g rounds as it has a thin section near the extractor cut out.

    back to the discussion on how to strengthen the 7.62x39 bolt--

    if the extractor was made a bit thinner--giving a little more meat for the lugs to hold to the bolt? would the extractor still be functional???
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