I assembled an AR-15 a couple months ago. Ruger Elite assembled lower, PSA 5.56 1:7 twist 20 inch barreled upper. I mounted a Nikon M-223 mount and M-223 scope on the gun.
First range trip was with 55 grain .223, just to get somewhat of a zero in. Groups at 100 yards kinda sucked, but that's what I would expect.
Second range trip with 75 grain 5.56, and the groups got worse as I shot. I didn't realize like a dolt until after I was out of ammo that my scope mount had loosened off of the rail. When re-tightening, the damn screws stripped out.
Third range trip I have a new scope mount torqued to spec with Loc-Tite applied. I have 75 grain .223 ammo. I get a zero, and while making adjustments I'm getting some wild groups. Three shots would be somewhat close, I'd make 1 or 2 click adjustment right (.5 inch at 100 yards), and the next shot would be 3-4" right. Next grouping would still be pretty sloppy, a couple close and another a few inches off at 100 yards.
My fourth range trip will be today. I took the scope with mount off today, and the screws even with Loc-Tite didn't take much effort to remove. I mounted my EoTech holographic sight on the gun, and I'm going to see how it groups with .223 55 grain ammo. Assuming I have reasonable groups, even though it's not the best ammo choice for the barrel, is there any way to determine if the scope is bad or the mount is bad any other way than swapping parts and seeing what changes? I will say so far I do not like this scope mount. I have the M-308 scope on a Remington 700 with rings and it's a 1 MOA rifle. I have a feeling it's the scope mount, but I'm looking for a potential shortcut to determine that before buying more stuff. I do realize it could be the PSA upper as well, which is why I'm testing it with a different sight today.
Thanks in advance.