I saw this new S&W M&P Sport II OR rifle on GrabAGun.com
for $499. Is this the same or similar to the OTHER OR M&P AR?

Smith and Wesson M&P-15 Sport II Optics Ready Black 5.56NATO / .223Rem 16-inch 30rd

Similar, not the same. The regular OR has the M4 barrel with the cutout and chrome lining, this has the Sport barrel with no cutout and melonite coated barrel. That's basically the difference.

This is new the Sport II OR, I guess they install a railed gas block instead of the A2 post on the Sport II.

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Still carrying my S&W 642