I have a 5 year old 7mm-08 plastic BAR. 1st 2 shots are very decent. about 1", I'm happy. After the barrel gets warm, and then hot, the shots start stringing in an arc... like a crescent moon. 4-5 inchs off center at 100 yards. If I let the barrel cool down, the shot returns to center. I know it's a hunting rifle, not a range gun. But I like to sit at the range practicing for hunting season. and put 20 rounds though a sitting. Can these guns be smithed to be accurate when hot ?
Not too many will touch the trigger because apparently, there is a fine line between semi and full auto when it comes to this rifle. I shot a bit with my .308 today and it does go from 1 moa to like 2 once it heats up... no where near what you got ... maybe you should check the forearm lug.
2 years later... I never did anything about the 7mm-08 stringing. I did buy a .243 BAR, and it is deadly accurate. Even when hot. I shoot 300 yards. 200 yards all day. Maybe I got lucky and found the right ammo. The 7mm-08 needs to go to a gun smith.
I have a bar shorttrac in .308. I was obsessively ocd about breaking in the barrel, slowly shooting 20 rounds and cleaning between each. I made sure the barrel never got hot in between rounds and it is a tack driver with the right ammo. However, like all my european made rifles, they shoot copper loads like Barnes and Hornady gmx like poo.