Was out at the range dialing in my new scope on my AR15. Had the gun on a front rest and sandbag in the rear and got is zero'ed and then all of a sudden it was shooting about 5-6" high at 50 yards. I finally figured out that when I had the hand guard sitting on the rest it shot really well (less then 1"groups at 50 yards with factory ammo) but when I inadvertently had the front of the gun sitting on just the barrel it was shooting about 5-6" high. I went back and forth several times and it was doing this consistently. Being new to AR's and rifles in general is this normal or do I have a problem with my gun? I suspect I need to re torque the barrel nut but if it was loose and moving around I would think my shots would be all over the place.
This is a home built AR, mega billet upper and lower, spikes barrel, midwest industries hand guard.