Congrats on your new S2 Vanguard. I agree on the 55 grainers probably shooting small groups. Actually your 1 in 12 should handle all the ammo lighter than 55grs and give you great groups.You won't have to settle on just one bullet weight
. My.223 shot the FMJ, the hollow points and the soft points 55 and under with great accuracy. The 1 in 12 doesn't usually lend itself to the longer bullets (heavier bullets) but every rifle barrel is different and yours may go for a couple of the heavier bullets. (some of the nation members have had luck with the heavier bullets in their 1in12 rifles, so you'll just have to try a few of them to find out) Anyway let us know how she shoots later on, and have fun at the reunion. Be safe