I just bought a new AR with a 1/7 twist, what grain of bullets do I need?

ammo-oracle.com/

You can use the Greenhill formula to determine the proper bullet to twist ratio... It is based on the rule that the twist required in calibers equals 150 divided by the length of the bullet in calibers...

This can be simplified to:
Twist = 150 X D2/L (D2 = D squared)
Where:
D = bullet diameter in inches
L= bullet length in inches
150 = a constant

This formula had limitations, but worked well up to and in the vicinity of about 1,800 f.p.s. For higher velocities most ballistic experts suggest substituting 180 for 150 in the formula...

Thanks for the info, does anyone know where I can find a case or less of 67, 69, or heavier, besides Wolf ammo?

check the ammo forum