This is not an ammo, or bad range or bent barrel issue. Bad ammo will give erratic groups, not good groups but off the paper. This is a rifle that needs to be sighted in by someone willing to do a slight amount of work. Folks have been drifting rear sights for windage as long as there have been rear sights. I am sorry it is not as easy as clicking something, but the rifle you have is a 19th century weapon designed by and for folks who had a bit of self reliance skill.
Go to the range with a box of ammo from Walmart. Put up a target. Put up another target to catch the bullets since they are not going to impact on the one you are aiming at. Or use a big patch of butchers paper. You can undo a couple of brown paper grocery bags if there is no one left in your area with butchers paper since buying pre-wrapped meat is easier. Shoot a three round carefully aimed group off of a sandbag.
Use the notched doo hickey that holds up the rear sight and let it down a notch, this will lower the group. Shoot another group and repeat until the elevation is where you need it.
Place a dab of white out on the barrel and rear sight in such a way that you can make a witness mark. Or use tape. Drift the rear sight a slight amount and shoot a group. Repeat as necessary. With most 30-30 loads if you are on at 50, you will be on at 100 and a tad further.
This is simply the way it is. Do this, or some variant thereof, or get rid of the gun. There is no other way with those sights.
An option is to order an aperture rear sight, Lyman or Williams, from Brownells. Some of those are click adjustable. I have a Williams on one of my 30-30's and like it, but it is not click adjustable. You loosen screws and slide the sight. It's more streamlined.
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