Yes you can shoot 5.56 in a .223 Wylde that's the whole point of .223 Wylde is it shoots .223 Remington and 5.56 NATO perfectly fine. Unbranded AR is the manufacturer of the lower, it is polymer  

At this price no TRS26, just the rifle and mag  

MBUS and Sig Romeo MSR are extra. 

Open to offers and negotiation

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Sales tax charged, background checks conducted, must be 18 or older for long guns, 21 or older and OK resident for receivers and handguns, must have valid gov issued photo ID for background check.