So I have thought more about the BOSS system, and it is a barrel tuner. However, if the barrel is whipping at a certain frequency for a certain bullet, then the same weight/cartridge bullet could still fly out at the same angle each time you shoot. Having bullets fly out closer to the center line will make your shots appear more accurate if your target is placed perpendicular to the barrel. Think about it. The groupings would be exactly the same if the barrel had a consistent whip.
Now, a second possibility is that the barrel's vibrations are somewhat different from one shot to the next. This means that the bullets exit at different angles and by simply reducing the amplitude of that vibration by tuning the barrel, the groupings would be much tighter. I think this is probably the case with the BOSS system - it acts to dampen the vibration for a given round and cartridge.
So, the question is, does the Browning BAR, well maintained and in the hands of a good shooter (with proper sight mounts) provide enough accuracy to hit the heart of an elk (say 3 inches across) at 300 yards? Second question is does the BOSS make your gun look ugly??