My only exp with .243 is with a M 700. Can't say what the twist is.
But, it's a one holer with 100gr. and nearly so with 60s.
Only killed two animals with it so far, but, it's my antelope gun out here in CO.
Killed a nice buck three yrs ago at +_90yds. Too close to tell much about it.
But, was done at the shot, but, again, hit the spine thru the shoulders. I was kneeling thru
a fence afraid he'd spook so didn't want to lay down, or lean against the post. I wasn't very
steady and just fired when it looked right.
The other was a coyote at 75yds with the 60gr. Hit at the base of the neck sideways.
Made two piece's of that one. head and body separated. Pelt wasn't much good.
My belief on accuaracy is: get a bunch of bullets of different makes of the wt you want to use and
sort them. same load, different bullet, five shot groups. Compare the size of the group.
Do the same thing with each wt bullets you want to shoot.
Main thing, measure the twist of that bore. IF you can't find a chart anywhere, call or e/mail any of
the barrel makers and tell them what twist you have, and what bullet you'd like to shoot in it and they'll tell you whether that twist will shoot that weight or not. If not, they'll suggest what wt bullets
that twist should shoot best.
Wish you well,
George