I just watched your new YouTube video on bore sighting where you look down the barrel at a target 50 yards away, and dial the scope to the target. I have had this bore sighter for at least 30 years. It has a magnet and sticks on the end of your barrel. Nothing to stick in the barrel. You look through your scope and you see a target grid. You just adjust elevation and windage on the scope to the bulls eye on the target grid. Once I have done this I shoot a shot at 25 or 50 yards to see how close it is, make minor adjustment, the to 100 yards. For me it has always been a 2 or 3 shot sight in.
It may have been discontinued, but it appears Bushnell has the same type of device.