I just got a new EOTech 516.A65/1 in the mail today. It is replacing the EOTech 511.A65/1, which I bought several years ago and don't think L3 is making anymore. I just noticed a few differences between the two. Since I haven't seen these differences anywhere else, I thought I would list them here: The 516 is longer and wider. Not suprising, since it uses CR123 instead of the 511's N-type batteries. The 516 has an extended curled thumbscrew crossbolt knob. The 511 came with two crossbolts: one with a shorter thumbscrew knob and one with an allen head crossbolt for an even lower profile. The finish on the battery compartment was different. The 511 matched the adonizing on the aluminum hood perfectly. The 516's was more like the finish on my Glock slide. It was more textured and a little greyish. The lever to remove the battery compartment was much easier to open on the 516 than the 511. The 516's is narrower and and turns up at the end. The 511 was flat and very hard to get your finger under. The 516 has the 7mm raised base. It puts the iron sights in the bottom of the sight window. It gets the irons out of the way of the reticle. The problem for me is that is it raised too high. It blocks a lot of the apature. It leaves just barely enough sight picture to use. Its going to take some getting used to. The buttons on the 516 are mounted on the right side. The 511's are mounted on the back. I don't know if these are just differences between the two models or design changes that have been made in the last several years. I suspect the latter. Just FYI.