I was cheating and shooting M118 from a custom built Springfield Armory rifle. Old John in the shop is a magician. Stick with the Federal 168 when using the Springfield National or Super Match barrel. Just as good to 600 yards.
Here is a 5 shot group from 1200 yards from the Mk12 Mod01. I only shoot 5 then let the barrel cool down. I shoot 3 at a 100 yards to verify zero then move it on out. I blew through the 20 round M1A magazine to see how the rifle would hold POI after things heated up. Gotta love a big, wooden stocked, clunky ass glass bedded M1A!
That looks like about 3/4 moa w/ open sights and 20 rounds; unless my eyes are deceiving me??? And since you are verifying zero is there supposed to be a point of aim under that 3 shot group?
The lowest round (cold bore) of the 3 shot group was the blooper aimed at my intended POI. The 2 others were aimed right at a fat magic marker dot (intended POI, size of your pupil in bright light) under the top two impacts.
About one 7Up and half a bag of pretzels. Or about 10-15 minutes as I drive down range to check my target, admire the beautiful desert view, unpack my rifle once again and reload. I did an experiment and shot two 5 round groups in fast succession and the second group hit low. Not sure if it was the barrel getting hot or the air temp dropping rapidly. It was at sunset and the desert temps drop very fast once the sun goes down. Gonna go back out to a different spot next week if I can scrap up some gas money and see it what caused the drop in the POI. Curious minds want to know these sort of things. That dry lake bed is now under 2 feet of water. There is an old stone quarry on Stansbury Island of the Great Salt Lake that I can shoot at. Cross winds (1/2 value at 8-12 MPH) are pretty stiff, as they spot is right on the shore of the lake. Temps should be high 50's with any luck.