Charles, welcome to the board.
We are fortunate to have folks from the industry here to answer questions, simple and complicated alike.
The answer given was correct, a 1-8" twist allows you to use the heavier bullets, which should aid in accuracy.
Please take some time to look all over the board. There is a specific ar-discussion area, as well as an ammunition area.
Another place you may look, and this is just for some damn good info on 5.56 mm ammo is the Ammo-Oracle.
Link is here: www.ammo-oracle.com/
This is maintained by a few VERY knowledgeable folks on this board. Basically, it is the bible for infomation on ammo for the ar-15 platform.
Hope you enjoy your stay, and don't be a stranger.