Barrel tuners such as the BOSS have been around for a long time. Changing the weight's distance from the muzzle as much as .005 can make a difference.
Barrel harmonics can be very unpredictable, and I have tuned many Browning rifles that wore a BOSS to incredible accuracy. Hard to imagine a BAR in 7 mag dumping all the bullets in a hole.
When steel is made at the foundry, many factors come into play and barrel makers are at the mercy of what steel they get. Barrels can be very different from the same lot of steel.
When all is said and done, some barrels will never give an issue, some will with a weight on the end.
It is very convenient to stick the device on the barrel and run with it. Learn the limitations and influences, then enjoy the convenience. I just got a lab radar unit to replace my Ohler 35 P. There does not seem a free ride in making things easier. Seems like sales and marketing leaves out a lot of specifics and Marketing also makes general statements that would seem to apply to ALL barrels. The lab radar seemed like the most idiot proof thing you could come up with, but then there is the reality check when the blinders come off.
I know that barrels of mine that I put a muzzle break on can change the accuracy node along with the point of impact, how much is trial and error, don't assume anything Each barrel will be an animal in and of it's self to deal with. Seems like barrels with a lot of meat are less apt to small changes, and skinny whippy barrels are more unpredictable witches to deal with...just a rule of thumb.
What is dumb founding is that I have used the same muzzle break on 5-6 barrels with no ill effect, then one barrel would be in the twilight zone with accuracy. I always test 10 rounds without, then 10 rounds with it on.