Well, I have been in your shoes before and I'll probably be there again.. It can be frustrating. I guess I would start by asking why you choose the 123 A-max and the IMR4831 for this rifle. I think H4350 or H4831SC would be a more ideal powder choice. I also think you are giving up a little bit of BC with the 123 class projectile over say a 140 grain projectile and that also may help you get closer to the lands compared to the 123 Amax. However, if you got access to the IMR4831 and sitting on a bunch of 123 Amax's then I certainly understand that...
But back to you question on this particular bullet/powder combo.. You can really see the vertical dispersion on the 50.5 and the 51.0 load and I guess that is due to the high ES you observed. I'm not sure what happen with the 49.5 load since it had a decent ES but also show a large vertical spread. The group at 50 is the best at .902 moa but I'm not so sure I wouldn't chase the 51.5 charge even though it was slightly higher at 1.06 moa... I ran this powder bullet combo on Quickload but I don't know your OAL cartridge length and the case volume in grains of H20 but it appears that you are under pressure quite a bit.. You may very well find a good load down there and be great but just know that you got a little farther to go before you get to max pressure. There appears to be a node at around 52.0 grains according to QL and some rough data I've put in... If you want to send me your OAL cartridge length I'll try to get you closer. You will still have to play around with it to find exactly where its at...
I would shoot the same test but load 3 each from 51.2 to 53.0 in 0.3 grain increments... Thats 21 shots total and maybe a few sighters in the middle to take the cold bore shot out and get dialed in. Sorry for rambling but I hope i've helped you some.. Good luck with it..
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