I usually add a tension screw to the forend hanger.
Have you tried shooting it without the barrel band? If I have a no 1 or no3 that needs tuning I usually remove the forend and try for groups. I also use a wedge between the barrel and hanger pushing it in deeper looking for a sweet spot. If I find that helps I drlll and tap for the tension screw. Or you could try the Hicks device. The forend is another place to look. I have slightly relieved the barrel channel and where it touches the receiver. Usually the tension screw has done it for me.
