Finally made it to the range today to sight in my new upper for my SP-1. Rifle shot great for first time out, 16" Colt LW 1/9 barrel, SP-1 slab sided upper, Bushmaster bolt assem. Shooting Black Hills 55 FMJ, best five shot group was 2" with irons. My question is that to zero rear sight, had to crank it pretty far to the left with the sight tool for proper zero, still have some adjustment to go farther, but not much. Normal for A1 type rear sight? My 20" upper the rear sight is pretty much centered in the sight groove. Other than that this thing shoots damn good for that skinny little barrel, 5.5 lbs. with the collapsible stock!

Normal for A1 type rear sight?

No, it's not. Either the BBl is over torqued or the front sight post is off would be the two most common reasons for this condition.

As I recall I had a couple of A1s in the Marine Corps that I had to dial a good bit to the left. Could be trigger pull, could be barrel set, could be the crown. As long as it works & you're zeroed, you're fine IMO.