Depends on the size- it could be .440" dia, which is about 127 gr, or .445", or even .450", depending on your barrel.
Green Mountain barrels tend to run large-a .45 cal can accept a .450" ball, and a .50 cal can accept a .500" ball. Does that mean a GM .45 is really a .46? Or a GM .50 is really a .51? I've been wondering about this.