I've noticed that some people who have issues lining up prone also suffer from inflexibility of the thoracic spine (myself included). A small foam roller has helped my increase flexibility enough to use my upper back and decrease tension on my neck.
I used the accelerators back in the late 80s in my 30-06. Around 100-150 they were fine, minute of groundhog. When I tried them at 400, I used the whole box and never hit. More like artillery at that range.