Last time I ran my AR was in a class in July, since then it's just been used for some dryfire drills but mostly sits in the safe. Today I got it back out to the range to test some loads, and found that the optic was wildly off. left/right was fine, but elevation was off by 5-6" at 100 yards. Once dialed in we played with various magnifications and didn't see a huge POI shift at 1x, 4x or 8x other than my eyeballs not seeing the same spots on the 50 yard test target. Vortex Strike Eagle 1-8x in the vortex mount. Hasn't shown any issues up to this point, about 3000 rounds through the rifle since mounting. Capped turrets, so nothing would have gotten bumped. Everything has lock tight on it and I verified nothing was in the slight bit loose when I checked the torque at home. Tried a 5 different loads (4 factory, 1 handload that works very well, btw), and they all shot about the same with respect to elevation being off. So, optic failing? I got it too hot at the class and warped something (420 rounds over the day with lots of pistol transitions and shoot house stuff so not too punishing on the rifle)? I shouldn't have cleaned it? It did have new gas rings in before the class, and I didn't check the zero before the class... so ? Can't have changed the velocity that much! Hand guard is free float and the screws are still torqued (and lock tighted). Ideas? Things to check?