Sport v. OR differences:

Barrel - OR has a 16" 1:9 twist, 6R rifling, chrome lined barrel and chamber. Sport has a 16" 1:8 twist, 5R rifling, melonite treated (surface hardened) barrel and chamber. Both use 4140 barrel steel.

Upper receiver - Both use 7075 T6 aluminum and have flat top with T marked rails. Sport upper receiver has no forward assist or dust cover. OR has both. Both have casing deflectors. Sport (and I assume the OR) have M4 feed ramps.

BCG - Both have chromed lined bolt carrier and gas key. I suspect that the BCG's in both are identical, based on my inspection of the BCG in my Sport.

Flashhiders - appear to be identical.

Sights - OR has none. Sport has an F marked front sight base with an A2 adjustable sight post and a detachable dual aperture rear sight.

Lower Receiver - Both are forged aluminum. The OR has the straight bottomed hinged trigger housing. The Sport has an integrated bottom trigger housing that is enlarged and curved.

Stock - Sport has a six position telescopic stock. OR has a six position CAR stock. They look identical, so I'm not sure what the difference is.

Hand guard - They appear to use the same hand guard, but the specifications don't state what type of hand guard either uses. They look the same in the pictures.

I think that covers all of the working parts. Not sure if there are any other differences.