It's possible to do it yourself if you can look thru the bore from the breech end. I remove the breech plug and place the rifle in a vise. Look the the bore and line it up on a distant object that you can center in the bore. At night, a light in the distance works, or during the day, an orange laying in the lawn. Once the object is centered in the view thru the bore, adjust the reticle so it is centered on the object. Have done many rifles this way, both muzzleloader and breech loaders. This is good enough to be on the paper at 25-50yds, sometimes even at 100yds!