I can reach out to 400 yards with a good fiedl rest and print sub 2" groups with my 338 WSM XP-100.
This handgun will drive the 210 gr Partition to just shy of 2800 fps. It has noticably more power then a 338-06 in a rifle.
I do not feel much of a handicap with this handgun at ranges out to the 1/4 mile mark.
If you don't mind, could you send me his contact info as well.
My e-mail address is firstname.lastname@example.org