There was a guy on the forum who shot several elk at 900-1100 yards with an A-bolt in 300 WM. He was/is a benchrest shooter and knew how to develop loads. Name was Goodgrouper. He used a Leupold V3.
I have an A-Bolt M-1000 Eclipse in 7mm WSM. When I use factory ammo, groups < 1.0 MOA groups at 100 yards were few and far between. When I started handloading, and applying a lot of the information I got from this forum, I found rifle shoots better than I can. Now, < 0.5 MOA groups are not unusual at 600 yards.
I have owned two A-Bolts - and both shot under 1 MOA out of the box. While it is possible that it may be your barrel, I would first take a hard look at your scope. Leupold makes a great scope for the $$ invested, but I have had to return a couple of VX-3's in recent years because they would not hold a zero (crosshairs were moving on me). If your scope turns out not to be the problem, then I would replace the stock with the Bell & Carlson and bed it. Be sure and let us know how things turned out for you.