I have never owned a guide gun, but a friend of mine has one in 450 marlin. I have shot it with factory ammo, 350 gr., from a kneeling position at 100 yards with factory sights maintaining about 2 inch group. I own a new model 444 Marlin with a 22" barrel. I have re-worked the rear sight with a flat file to help these old eyes. I have also coated the front sight with blue mirrobright fingernail polish. With the factory Hornady 265 gr. flat point at 100 yards, in the kneeling position, I am maintaining groups less than 2" and am very happy with this gun. I am getting ready to reload for this rifle, but I don"t think that I will be able to do any better accuracy wise. Maybe a younger man could.