I had the same problem with the AT-One, but with a Browning X-Bolt. I don't remember if it was binding when I received it out of the box, but the barrel wasn't floated and had some pressure points I didn't like. I took it to a "gunsmith" to have it bedded. Terrible job. First thing I noticed was the binding with the bolt. So he just loosens the rear lug screw a bunch...see, all better now. Wrong answer. Took it to another "reputable" gunsmith who completely re-did the bedding job and everything is perfect now. Somehow that rear lug screw was the issue with the bolt binding up. Nothing to do with the ammo or being dirty.