I was at bear den several times and we allways used 12G doubles with great success. I have heard about some missfortunes at dens, when people used rifles of medium calibers.
Now we just talk here about ideal gun for bear at den and everybody agree it has to be double rifle of big caliber with medium-slow velocity bullet.
Unfortunatly Russian Artemida DR 45-70, known as Remington Spartan SPR-22 and all this project seems fell through.

Geno.