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Thread: How does Law Enforcement manage to get by with M&P15s?

  1. #61
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    @Echo40 : Thanks.

  2. #62
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    Quote Originally Posted by the AR-15 Junkie View Post
    Wonder how many M&P rifles S&W take back in for repair under their Lifetime warranty?
    I thought warranty was a year, then the lifetime service policy kicked in. Not sure, though.

  3. #63
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    Quote Originally Posted by pinzgauer View Post
    Same for 6061 receiver extensions versus a forged 7075. Most of us have been around or seen receiver extensions fail. Usually from misuse like mortaring or similar.
    1. Arrange in order of strongest to weakest in bending:

    a) M1 Carbine stock at the wrist
    b) AR with a 6061 receiver extension made to “MIL-spec” dimensions
    c) AR with a 6061 receiver extension made to “Commercial” dimensions
    d) A 24 inch long piece of 1-1/4 inch beech dowel

    2. How much force applied to the end of a 6061 receiver extension at a right angle is required to put a permanent bend in it?

    a) 250 lbs
    b) 350 lbs
    c) 450 lbs
    d) 550 lbs

    3) How much force is required to shear the threads off a 6061 receiver extension screwed in to a 7075 lower receiver?

    a) 1 ton
    b) 5 tons
    c) 10 tons
    d) 15 tons

    4) Why is it impossible to shear the threads off a 6061 receiver extension screwed into a 7075 lower?
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    5) During normal operation, where is the highest stress seen on a standard carbine receiver extension.
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

  4. #64
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    Quote Originally Posted by lysander View Post
    1. Arrange in order of strongest to weakest in bending:

    a) M1 Carbine stock at the wrist
    b) AR with a 6061 receiver extension made to “MIL-spec” dimensions
    c) AR with a 6061 receiver extension made to “Commercial” dimensions
    d) A 24 inch long piece of 1-1/4 inch beech dowel

    2. How much force applied to the end of a 6061 receiver extension at a right angle is required to put a permanent bend in it?

    a) 250 lbs
    b) 350 lbs
    c) 450 lbs
    d) 550 lbs

    3) How much force is required to shear the threads off a 6061 receiver extension screwed in to a 7075 lower receiver?

    a) 1 ton
    b) 5 tons
    c) 10 tons
    d) 15 tons

    4) Why is it impossible to shear the threads off a 6061 receiver extension screwed into a 7075 lower?
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    5) During normal operation, where is the highest stress seen on a standard carbine receiver extension.
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
    Ok, but whatever force a 6061 extension can take before breaking, the 7075 extension can surely take more, no?

  5. #65
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    Quote Originally Posted by pinzgauer View Post
    Same for 6061 receiver extensions versus a forged 7075. Most of us have been around or seen receiver extensions fail. Usually from misuse like mortaring or similar.
    I thought the RE failures were largely due to the thread cut method on commercial "tubes"... not so much the material.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

  6. #66
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    Quote Originally Posted by lysander View Post
    1. Arrange in order of strongest to weakest in bending...
    I understand the point you're trying to make. That said, it's still just a very complicated way to say "I think 6061 receiver extensions are strong enough for what LEO needs".

    And your opinion would count for a lot in that, you know more about materials then just about everyone else on the forum.

    But I could equally ask "if 6061 is sufficient, why did the military specify for forged 7075"?

    We know the somewhat bogus reason they selected c158. We also know why they wanted 4150 CMV and why that may not be relevant to semi-automatic patrol carbines carried by Barney Fife.

    I'm electrical engineer but I have enough mechanical engineering and physics background to understand why forged is stronger than cast/extruded, rolled threads are stronger than cut for the same base material thickness, etc.

    But we're approaching this whole discussion from two completely different directions:

    Your perspective seems to be they probably didn't have enough money to buy a real milspec carbine, so they bought one that's good enough for a weapon that will be carried a lot and shot very little. (Yes I know they're semi and not really mil spec but we're talking about materials here)

    I'm looking at it from the perspective of this is a manufacturer which has clearly used cheaper materials, sometimes bought some high quality parts and sometimes bought from a commodity manufacturer, and there's no easy way to tell which is which.

    And for me that ends up as false economy as you can spend 10-15% more to get a known quantity.

    I want maximum value for my money and part of that means getting the best I can for the same dollars.

    If you were to apply the logic that we seem to be debating here to service pistols the wailing could be heard around the world. Echos of SW99 vs Walther P99/PPQ. Throw in some Canik parts because they're dimensionally the same and should be okay, shouldn't they?

    Likewise, I have first hand knowledge of what local departments are spending on communication equipment and it's staggering. Well beyond the realm of the required functionality.

    You could buy 20 Colt service 6920ish carbines for what one radio and docking kits for an officer cost.

    So the monies there if they want it.

    Probably got a grant for it and much is Federal money or something like that, and there's probably not grants for carbines. I get it.

    I understand you have a vested interest in the S&W brand, owning one. I'm sure it's a fine rifle. I have 4140/6061 carbines that have been very reliable.

    But I try to buy a little better now, mostly starting with LMT defender lowers If not Colt 6920s. I don't lose sleep over this, but I find I can usually get better quality materials for roughly the same price as the commodity stuff.

    We've probably taken this as far as we can, and I respect your opinions on materials. It's good to know the 4140/6061 stuff is probably going to keep working :-)

  7. #67
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    Here's the thing, a 7075 mil-spec type RE is like what? $40? That's the price for us consumers. I'm sure gun manufacturers can get them for cheaper. I'd be willing to bet that 99% of the members on this forum would choose a 7075 mil-spec receiver extention if they were building their own hard-use rifle from parts. A commercial grade RE may very well be quite strong, but I think it's a known fact that the military type 7075 RE is stronger. So why not use it? They're not hard to come by and they're not expensive. It's just a sign of cheapening out. A cheap rifle with cheap parts cutting corners to save cost, and passing along an inferior product to the consumer.

  8. #68
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    Quote Originally Posted by pinzgauer View Post
    But I could equally ask "if 6061 is sufficient, why did the military specify for forged 7075"?
    Because Stoner was not a metallurgist and defaulted to 7075 for everything.

    The magazine release button is 7075-T6, please explain why the button needs to have a higher yield strength that the steel arm it is screw to? (and about twice as strong as the forward assist plunger)

    When Colt re-did the drawings, they fixed all the steel material call out to reasonable choices 11XX steel for things that are not stressed, and good steels for those that do.

    But, Colt never made an aluminum rifle before, so they left all the aluminum specs are is.

    Also, please explain why the handguard slip ring needs to be 7075? Newly designed free float hand guards are stressed more heavily and manage to survive being made from 6061.

  9. #69
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    This is good stuff, you guys. Funny how many sacred cows are sacrificed on the altar of truth.

    Before you take down a fence, you should probably know why it was put up in the first place. Nice to hear from a guy that knows.
    “You have made us for yourself, O Lord, and our heart is restless until it rests in you.” -Augustine

  10. #70
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    Quote Originally Posted by lysander View Post
    Because Stoner was not a metallurgist and defaulted to 7075 for everything.

    The magazine release button is 7075-T6, please explain why the button needs to have a higher yield strength that the steel arm it is screw to?

    SNIP

    Also, please explain why the handguard slip ring needs to be 7075?
    All fair input.

    I for one welcome our new "good enough is good enough" worldview...

    This makes buying a carbine much simpler and we can delete literally dozens of threads where carbine X was shot down because of 4140 barrels or 6061 receiver extensions, etc.

    I can recall one recent one with 200+ postings about AR-10 REs.

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