AR 15 help

AR 15 help

This is a discussion on AR 15 help within the Defensive Rifles & Shotgun Discussion forums, part of the Related Topics category; I am new to the ar15 platform but am considering the S&W M&P15. What is the basic function, I've read a lot about gas piston, ...

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Thread: AR 15 help

  1. #1
    Senior Member Array fernset's Avatar
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    AR 15 help

    I am new to the ar15 platform but am considering the S&W M&P15. What is the basic function, I've read a lot about gas piston, blow back? It all sounds the same to me. What is difference between the SIG 556 and the mp15? Are they 2 differnt mechanisms? Is the M&P 15 a good beginner choice?


  2. #2
    Distinguished Member Array Tally XD's Avatar
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    The standard, or more common method, is gas blow back operation. What this does is uses blow back gasses to move the bolt carrier to the rear to eject the spent round casing and strip a new round from the mag and chamber it for the next shot.

    On an AR-15 gas blowback operates like this:

    - Direct Gas Impingement The barrel has a port hole, very small hole, drilled into the top of the barrel somewhere between the chamber and the muzzle tip. It is usually located under the front sight. The front sight, or gas block on custom models, is drilled to match the barrel gas port. Gas from the barrel enters the gas block and travels back through a gas tube back to the upper receiver. Mounted on the bolt carrier is the gas "key". This key fits onto the gas tube, which protrudes through the receiver by a little over an inch, and makes a seal. When the gas travels through the tube to the gas key this throws the bolt carrier back. The process starts all over again.

    Piston Operation is like this:

    - Gas piston operation uses a gas port in the barrel as well, but instead of the gas blowing back through a tube, the gas is directed to a piston rod that travels along the top of the barrel and enters into the receiver and makes contact with the bolt carrier. This backward force slings the bolt back. Since no gas enters the receiver through a tube, the chamber on the rifle will stay much cleaner and this, theoretically, keeps malfunctions down due to less residue and fouling.



    The Smith & Wesson Ar-15 is an excellent rifle for a beginner or advanced user.

    I am not really familiar with the Sig 556.

    I have not watched all of this video but it talks about the debate over DGI and Gas Piston.
    http://www.youtube.com/watch?v=6auXT...1&feature=fvwp
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  3. #3
    Senior Member Array fernset's Avatar
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    Thank you for the lesson. But for some reason youtube wont let me see his vids.

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    Member Array charlie1826's Avatar
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    As luck would have it one of my co-workers just bought a new Sig 556. I don't know if he has had a chance to shoot it yet, when I find out I will pass along the range report. Tally pretty much covered the rest.

  5. #5
    Senior Member Array fernset's Avatar
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    Quote Originally Posted by charlie1826 View Post
    As luck would have it one of my co-workers just bought a new Sig 556. I don't know if he has had a chance to shoot it yet, when I find out I will pass along the range report. Tally pretty much covered the rest.
    I'd be interested to hear bout it. Are piston ARs still pretty rare? More then a couple?

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