Best worst group?
That depends.
I got an Arisaka in 6.5mm, tried it out with some Norma factory stuff I picked up at a gun show. REALLY OLD Norma. The rifle put 5 under a nickel at 145 yards, iron sights, and I had a witness there at the time.
Well! The rifle can SHOOT!
Time, obviously, to see what it will do with handloads.
So I got the dies, laid out serious money for some Swedish match bullets, loaded ever-so-carefully and went out to the range.
At 200 yards, off the sandbags, I got a 10-yard-vertical by 20-yard-horizontal group.... with a couple of flyers.
The hard-jacketed Swedish match bullets were exploding about 20 feet in front of the muzzle. Seems that that old Metford rifling in the Arisaka REALLY distorts the bullets (they come out almost square) and the hard jackets can't take it, even though they shoot brilliantly in my Swede Mausers.
Went to the El Cheapo Remington 140, which has a fairly soft jacket and groups shrank a whole BIG lot! Right now, the old thing is about 1 MOA, which is where it should be.
Lesson learned.