I don't believe that 6BR is a round
commonly available on store shelves, is it ?
Unlike the rest of the comparable .22 caliber cartridges (.223 Rem/22-250/22 Nosler), nor is it a cartridge that factory rifle makers chamber many guns in.
I think the point is, it's a .22 caliber cartidge that easily fits Stanag mags but outperforms any other factory .22 ammo available.
And it has ballistics that are
similar to much larger cartidges (6.5 Creedmoor), but with half the recoil.
https://www.youtube.com/watch?v=EeMpd2qAY94