It's fairly easy to find out if heating is the problem...just wait 5-6 mins between each shot. This time should allow the barrel to cool to a uniform degree between the shots. I have not worked with the latest version of the BAR but sounds as if the barrel is getting hot (doesn't have to burn your hand) and is growing. The barrel will actually get longer as it heats. This combined with the taper on the barrel touching something can apply pressure which can cause the barrel to warp (or simply viberate a bit differently). Very small changes in barrel harmonics (vibrations) can cause groups to open and as the pressure changes the variations can cause wildly vaiable grouping. Try some slow fire groups see if that helps.. Unfortunately it is also possible the barrel was not properly stress relieved when it was made. Barrels build up a lot of stress in the steel as they are being manufactured. Normally these are removed after the barrel is complete and sometimes during the manufacturing process. If not done the normal heat built up by the firing process can cause the barrel to warp. This will be a very small amount but can do disastrous things to accurracy. If your problem does not occur when firing the rifle slowly and the weapon is new, I would consider sending it back to Browning.. I've excellant luck with their service department.. good luck from the gunnut69