Hi there. Your .500 S&W mag is perfectly good, and its cylinder symmetry is correct. If you look at the photo you provided carefully, you'll notice the triangle drawing is not symmetrical, because its center line is not perfectly straight, and not hitting the center of the concave (the human eye can easily be fooled). If you were to move the triangle's center line to the left slightly, the triangle will be closer to being perfectly aligned. The top of the center line is slightly closer to its right. I measured it, and the line needs to be moved slightly to the left to be symmetrical. Your gun is fine.