The 6.5x55 is inherently very accurate !!
Original military load would be 156 gr.
Use a powder that burns like 4350 and use a 140 to 160 bullet .
Get the proper cases not the stupid American ones .They had the 260 why screw up the 6.5x55.
Make sure the crown is OK.
Trigger was a very good idea.
When I made my custom 6.5x55 first try gave me 7/8" groups with iron sights !! Didn't go farther as it was a hunting gun which I used for deer for 25 yrs ! 140 , 4350 all you need .