I bought a new Faxon barrel for my AR10 in 6.5CM. I also got a new scope for Christmas so I was out sighting in and a cease fire was called. I ejected the round that I had just chambered and noticed this spiral on the projectile. I am sure that I have pulled other 308 and 6.5 rounds out of AR10’s, but I have never noticed this before. After the range went hot I charged the gun and pulled the round out without firing. The spiral turns in the opposite direction.
So my guess is that the rounds are spinning about 10 revolutions as they pass over the feed ramps as they leave the magazine. The reason that the spirals are reversed is because the AR magazines are stagger stacked and each round came from opposite sides of the mag. Being that I have never seen this before I am wondering if the barrel lugs are abnormally sharp, a different angle, different size or some combination of the above.
Has anyone else seen this? I will contact Faxon to see if this is an issue with their barrel, but I wanted to see if this was more common and maybe I just never noticed. It did not seem to impact accuracy too much, I was getting sub MOA with cheap factory ammo.