Ammunition is very important. For silhouette you need to group test it at at 100 meters. The group should be one inch or less.
You should test many different varieties and lot numbers. When you find the ammo that matches your rifle, purchase as much as you can, it is great to have a couple years worth stored up.
We typically test ammo off a bench in 5-10 shot groups, pick the best two and then re-test those. Try to test when there isn’t too much wind or mirage to effect the bullet.