Dano is right - this sort of forward mounted scope generally is done using a handgun scope. It's a lower power solution (usually a 1-N or 2-N scope, with N being anywhere from 4-8). Supposed to be faster acquisition, but I've never used one long enough to get really comfortable with the system. For something like a true scout rifle, I'd be far more inclined to go with a very high end peep sight, as those are extremely fast acquisition and offer good performance at dangerous game ranges. Some people swear by the scout setup, though, so maybe I'm just not giving enough time to working with this design.
I can't imagine the fireball that 20" barrel makes with a 300Wby round! Shooting it at dusk would be some kind of 'enlightening' I'd guess.