The single point attach with both sling ends at the grip is how I carried my 460 last year. The 2 point attachment is much better. You can lock in for a steadier offhand shot this way.
To try it tie a loop of 550 paracord around the base of your rear scope ring under the scope and attach to that. Carry so that the strap runs from the grip - under your trigger hand - over the shoulder of your off hand. The gun lays flat muzzle down and pulls up smoothly. You can brace firmly into the gun if the strap is properly adjusted.
"Therefore go and make disciples of all nations,... "
Handgun hunter since 1979 - haven't used a rifle since!
HHI member #992, NRA, SCI.