Well, after having this rifle for nearly three years and never being able to find a decent group for it (I even bought a second Arisaka just to have a rifle that actually hit what I aimed for) I have come up with a load to fit this ugly rifle.
For ever shooting this rifle to get to improve I would try jacketed as well as cast. .308-.312 sized 150-185gr bullets; they all shot all over the target and sometimes keyholed the 50 yard target.
I finally got tired of it and sized down some of Lee's 8mm (.323) 170gr roundnoses through a .314 sizing die. It made the driving bands pretty fat and the grooves pretty shallow but since I lubed them with Liquid Alox and did again after the sizing I wasn't concerned with a lack of bullet lube. (Honestly, I was resizing the bullets for my 88 Commission Rifle but I had some extra bullets and figured I give it a shot)
Loaded them with 12gr of Red Dot in some reformed 8mm cases (to 7.7 JAP) with standard winchester Large Rifle Primers. Seated the bullet at the first driving band and loaded up my first five for 50 yards. Not expecting to see any major change in the quality of the load (The rifle was going to be regulated to parts for the second Arisaka if it didn't work this time) I just quickly shot the five offhand and was surpised to find not only were all five on the target with no keyholes but that two actually cut the 9 and 10 rings respectively while the remaining three were strung out horizontally from the first two shot's at the three oclock position. Five quick offhand shots at fifty yards were all in the black!
So basically, in exception for the jerk behind the trigger who jerked off the five shots (Trigger squeeze ), this rifle finally has a bullet that it likes!
Bruce