I've bore sighted some and been very close, and others been quite a ways off. Usually it's the gun, not the equipment that makes the difference. Where they look and where they shoot aren't always the same. Ammo also plays a large part.
This is exactly what I have experienced. I have one of the magnetic-based laser bore-sighters and like it better than the ones that poke down the barrel with a plastic mandrel.
The one I have has a spring-loaded plastic cone that centers it with the bore, just as the magnet starts to grab. I am hoping some day for something similar with an electromagnet that you can switch on or off. A longer cone with a series of common bore-sized steps would also be good.
I have a door-less shed in my back yard with a target on the back wall, inside. The target is 25 yards from my shop, and it works out very well with laser bore-sighters as the distance is about right, and the target is shaded, so the laser dot is easy to see through a scope at any time of day.
Scope height makes a noticeable difference on the elevation accuracy that you can expect at that range.
One time I laser-bore-sighted a scope, and it was almost perfect at 100 yards when I went to sight in the rifle. I only had to adjust an inch or so to the left. When I saw that, I remember thinking that I really should have bought a lottery ticket the day that I laser bore-sighted that thing.