I agree with what has been said above.I use a bolt without a scope knowing that I am at a disadvantage.I just find it more of a challenge.Aside from leopard I shot all of the game I hunted in Africa without a scope.As for which is more reliable and accurate-a bolt or a double, based on the experience I had with two doubles I would say a bolt.I know where my bolt will put its shots without question.I can't say the same for my doubles.It could be that I do not own a good double-one that is accurate and stays accurate(and regulated).I don't trust what I read about other peoples experience with doubles because they are conflicting and no-one wants to offend the people that sell them who hangout on hunting forums.It also seems that no-one owns a rifle that doesn't shoot well.
