Sure, I see it's usefulness. But 20 bore is awefully wide for that weight meaning it would have no density at all so penetration would be very poor. In my opinion it would not compare well to a 650 grain bullet. But I think it could be great for hunting medium size game and as you mention, the cost is far more affordable than most .577 double rifles. I am sure it would be fun to load for and shoot, but I would not compare it to the .577 rifles, only speaking for myself.