This is just a shout out to SiteLite customer service. Like a dumbo, I didn't put silicone or Vaseline, as directed on the o ring for the spindle, while sighting in a 5.56. So, when I put it in the barrel, no biggie. But pulling that sucker out of the AR barrel, I ripped the small o-ring. Sighting the 300 PRC no problem due to a lot thicker o-ring. They sell an OEM complete o ring replacement on several sites for $12.99. I called SiteLite and he offered to send out 10 of that specific o-ring at no charge. He said I'm not special, that they do it for anybody that calls in.