I have an MMS marked Mega upper that had a canting Troy BUIS and a canting EOTech 512. The new Troy clamp fixed the cant, but my EOTech still cants, even after trying different clamps and both style cross bolts. I noticed that where the Samson meets the upper, you can clearly see a difference in the 1913 spec rails. They are the same width and height, but the angle of the bottom side rails are different. The upper has a quite a bit steeper angle on the underside and I'm wondering if it is out of spec or someting. Has anyone else noticed this difference with Mega or other uppers in relation to their FF tube? Both are suppose to be 1913 spec, but there is clearly a difference here.