I just checked my broken demo 511, a new in box 551, and a new in box 552

i used a dd rail, flat on a table, it was perfectly leveled, I had no discernable cant on any of those 3 sights, i did some measuring and they all seem square to the world, but i can tell you that i at one time put one on a rifle and it seemed crooked, i removed and reinstalled, it was fine then, i have no idea why, it must have been me

i will be looking at all of them as they come in, i sell a lot of them, and if i see one that lookes wrong i will let dennis know about is and we can see what is up, but i have never had a problem with them

I do know that if the lower angled portion of the pic rail is off even the slightest on the ejection port side of the reciever, when you put the sight on and tighten it down it will let the mount/optic pull up on the ejection port side of the optic and will make it cant, i did have an out of spec reciever at one time that gave me fits, it was made wrong, i am not saying anyone has anything bad here, but i am in the buisness and have seen a few bad parts from all of the manufacturers at one time or another