You need to read up on this issue. There's plenty of information available. Monometal bullets just aren't for double rifles. They can and do cause barrel damage. DR bullets need a compressable (lead) core.

The usual damage is overstressed rifling, and it's very common. A friend of mine who is constantly shopping for double rifles sends his "prospects" to his gunmaker before finalizing the deal. Two of the last four turned out to have overstressed rifling. I ruined one myself with Barnes X.

The problem with OSR is that, while the problem is well known, few actually know what it looks like. I know several very bright, experienced DR guys that have spent a lot of money on DRs without knowing that the barrels were damaged. This also leads many to believe that they've gotten away with it when they haven't.

Some believe that the problem is confined to older rifles, which isn't true. Some also believe that "banded" monometal designs (which the A-Square is not) are OK, which I think is wishful thinking.

The other common type of damage from monos is the barrel solder breaking loose.