I have the 5 groove 1:8 twist PacNor.

any twist 1-9" (or faster) will be fine with those bullets

Outlaw,

The standard with US makers is the 6.5/9" twist. My 6.5-'/06 is a 9" twist Shilen, and it will shoot 140s of whatever shape factor well. I have shot up to 165 grain bullets from it, 165 semi-spitzers weren't properly stabilized. Anything shorter than those fly well (and accurately, this rifle is quarter minute with its best loads).

I don't even know how many lands and grooves there are in my barrel, whatever Shilen likes I guess. There are theoretical arguments as to the best number, but I haven't been convinced by data yet.

I would like to read any such data.

jim

Well

The greenhill formula will say that 1-8,5 to 1-8 will be fine for the 140's. I know some rifles with 1-9 that havn't shot the 140's that well and had some problem with the bullet stability.

I have used 1-8,5 and if you have to choose, the 1-8 is best.

/ JOHAN

6.5mm (.264") Twist

3 groove 8" 9" 10"
4 groove 7" 8.60" 11"
5 groove 8" 9" 12"
6 groove 10"
Polygonal 8" 10"

These are from PAC-NOR
which one for 120gr-140gr bullets in a 6.5/06?