So I have a Eotech 552 on a M&P 15t, I sighted it in a few monthes ago. I put it away had not shot it since. The other day I got it out and my eotech didnt seem so sighted in anymore. The case I had the Ar in was moved around some but I would not say beat up or anything. When I sighted it in I used Rem UMC and the other day I was shooting Brown Bear. Is there a drastic diff between the two?? I was shooting at a little 2-3" stick on target, from about 40-60 yards away I didnt hit target once. There was a nice tight group about 2 inches lower but could of been from a previous shoot. I thought eotechs if nothing else would hold zero due to their design and extreme use in the mil. Sorry for the book. Just left me feeling a lil steamed. Ever heard of this??