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sig m400 extension tube

  1. Sig M400 Extension Tube Mystery

    SIG Sauer Rifles
    I recently purchased the M400 in Mass and in the process of upgrading parts I made the assumption that the extension tube was Mil-Spec based upon reviews, product manuals and a call to verify it with Sig customer service. Silly me to no measure. My Mil-Spec stock didn't fit so I then measured...