I have an AR 30 Lapua 338. The fellow I bought it from worked up the following load... Lapua cases, 89gr of RL25, Fed 215m primers, 300SMK seated at 3.75.
I have not shot it beyond 700 yards yet, but it seems to do well to that distance.
Start with H1000 and Retumbo. Max loads worked the best for me. I get 3150 fps avg. with the 250 scenars and 100 gr of Retumbo or H1000. These loads avg under 3/8" at 100 yards and is the hammer of Thor on mule deer!!!!
My ar30 liked 98 gr retumbo 250 smk but I went 300 smk and 94 gr of retumbo. Both went under 1/2 moa 5shot groups at 100 yards. four inch 3 shot at 1162 my best on paper at that range that was with 300 gr smk.
my ar 30 just sucks! 3 to 5 inch groups @ 200 I tried every load I could think of . I even pulled my nightforce off my 308 thinking it might be my scope. It still shoots bad.