They have to mean capacity, because that would be true for round count. It is not true for energy of the round. The 460R is a fine cartridge but does not quite make it to 454 Casull territory in terms of potential energy.
"Always place your clothes and weapons where you can find them in the dark"
"Understand that the enemy is not the enemy in his own eyes ;this may offer you an opportunity to make him your friend. If not, you can kill him without hate, and quickly."