I have shot my 7.7x58 Arisaka every weekend after Thanksgiving for the last 5 years or so. Reloader 15 and 19 grouped my Hornady 150 and 170gr bullets well at 100 yards but I ran out of powder during the Pandemic to fine tune my tests. I switched to IMR 4350. This powder has worked well but again, I ran out of powder. I buy at local stores and the closest one I found is a 4-1/2 hour drive away and a pound of powder is $75. I plan to drive 41 minutes south and swtich to AA4350. The last I checked, it was around $50. I've tried 4064 in the past by my accuracy load included a heafty load and recoil. Reloader Powders had less felt recoil and IMR4350 was not so bad. A new powder I acquired is 2400 and will use these as follow up shot practice using Lee 170gr cast PC bullets.
The cases I use are LC and Norma. The only split necks I have acquired is because I didn't anneal the neck. I use RCBS dies and a Lee Custom neck sizing collet die. I get near zero runout using this die compared to using my RCBS die to resize a neck. My RCBS dies crush the fireformed shoulders on my cases, which I don't like. My first resized cases are sized to SAMMI length. My newly resized cases are just under chamber length. I use a Sinclair chamber length tool to determine the chamber length, managed to seat a Hornady 150gr bullet can touch the rifle, and shot rounds with various lengths from the rifle. Seating depth makes a difference. I wish my 174gr bullets could touch the rifling when seated in my extended case. I'll begin my tests again using AA4350 which is reported to be a good powder for the T99.
I sandbag and bench my rifle and have a odd way of lining up my sights because I think it's better. After placing the fore end on a sandbag, I raise the butt with my fist. But to line up the sights, I look over the aperture and line up the front sight under the target and lower my head onto my stock comb to reduce torque, then raise the stock with fist. I add pressure to the trigger like a handgun. My targets are made to help center my sights and get the best sight picture. I use a big red meat ball cut out of a bright colored cardboard sheet from the $1 store. A triangle in the same angle as the front sight ends with the tip on the center of the meatball. Two similar triangles point downward like a radiation sign so I can center the front sight better. I want to reduce error.