bruchi,
If you bought a complete Sig rifle, then you didn't get a cheap knock off rail. If the dealer made a claim that it was outfitted with a Daniel Defense rail, then he simply mis-informed/mis-lead you. It's not like it came with a chinesse airsoft copy or anything. The rail should have the Sig logo maghined into it on the left side rear of the rail. I believe that Sig has a notch milled into the upper where a corresponding tab on the rail fits in order to prevent rotation. From the looks of it the rail most likely uses a propriatory bbl nut and will require a wrench from sig. Just send the upper to Adco and let them deal with the dis-assembly.

