Sorry if my spelling is off… no auto correct on mobil and I have sausage fingers. In my oppinion bore sighters are better used AFTER sight in. Let me explain.
I have had great sucess bore sighting by setting up an official 100 meter small bore target at 50 meters. Remove the bolt or seperate the upper and remove the bolt assembly. Look through the bore and get on target. The just adjust the acope till you are on target. Fire 1 shot. Measure and adjust. Fire 1 shot at 100. Measure and adjust. Should be dead center.
Here is where the bore sight tool comes in
Setup a target in your house or yard after sight in. Aim dead center of the target. The red dot will usually be off center. Thats ok. Mark where the dot is with a pen for the rifle you are using and file the target. Now when you remove the scope or if you are a hunter and need to check zero, you need only to setup the target and make sure the reticle is dead center and the dot is where you marked the target. You can do this best by zeroing for 50 100 200 and 300 and marking the same target. That way you can adjust ypur scope before going to the range or verify what range the scope is set to.
Its a bit odd to explain…especially after getting 3 hrs of sleep then spending all day at a wedding with an open bar, but hope it makes sense!