Larue LT-129 Aimpoint Mount
I got this in to replace my A.R.M.S. mount. The ARMS was ok - when the screws holding the riser, and thus optic, on didn't loosen on me in the middle of firing, and if you never had to pull it off. The thing wouldn't repeat zero worth a lick.
The glass is held at the same height - co witness is a lower 1/3 for those that care. The cantaliever design lets the optic hang out over the D ring/barrel nut for a wider field of view of the area around you when firing. It also has a nifty spare battery holder built in.
The design itself is impressive. The underside has two machined lugs that engage into two picitanny slots. Side tension is done with a cammed lever putting pressure on the underside of the rail directly, no flopping levers involved here - and yes, the engaging surface of the lever is polished. The lever features a nifty safety on the end that clicks to make sure the lever doesn't come undone by accident. This is overcome by pulling the lever arm back a small amount, then opening it.
The repeatability is awesome - no changes in a dozen on/off cycles. The rings are precision machined and keyed/engaged to the 1 piece aluminum mount. Nothing to loosen on me or loose zero. Made in Texas, with a lifetime "give it hell" warranty.
To those looking to get into optics, and eventually upgrade - buy once, cry once. I certainly wish I did with the mount the first time around. I'm still running the first red-dot I purchased, an AimPoint CompC3, no magnification, 4 MOA. So far the optic has allowed easy hits from under 25 yards to 500 yards, and I have no doubt the mount will keep up to that kind of a standard as well.