Your group at 50 was great. The AMD65 12" barrel is inherently accurate because it is shorter/stiffer than a 16" barrel, but you give up some velocity. Also, the fitting of the gas tube along with the tight-fitting vented steel fore arm further stabilize the barrel. I had similar and completely unexpected results with mine - not as tight a group, but I had it sighted at 50 very quickly. In fact, when I later fired my SA85M with wood hand guards and got larger groups than the AMD65, I took a closer look and found the lower hand guard was not well-fitted, which I think allowed more barrel-whip. I changed the front end on that to the naked gas tube and vented steel fore arm (very tight) which instantly reduced the groups. If I ever go back to the wood fore arm on the SA85M, I'll have to build up the front tenon and fit it, which should give the same results as the steel fore arm.