"Zero" first or second crossing? Nikon BDC (rimfire)?

[rob350]

I have been trying to learn more about scopes recently and the theories behind more than just good old fun line up cross hairs, aim higher or lower, and pull the trigger and hear noise. Boom boom, the paper or stick is dead...

Now I understand the principle behind the bullet crosses your line of sight twice. But which is commonly referred to as your "zero"?
I understand that the old school mentality I hear from the older generation is something along the lines of a typical hunting round zeroed at say 50 yards (first crossing) it will also cross at say 200 yards. Or something like that depending on who says it and how much they had to drink that night at hunting camp...
But I suspect this mentality was built around the idea that you want to ensure you can make a quick shot at anywhere from 50 to 250 yards and always hit withing a "kill zone" area on the moose.

Being that bore sighting ignores gravity and only accounts for lining up your barrel point of view with your sights point of view at XX distance since the scope is mounted higher that your barrel, it would be "zeroing" for your first crossing.

Picked up a Nikon Rimfire 3-9x40 BDC for a 10/22. Now in order for this to work, the "zero" that you tell the software would have to be your second crossing would it not?

This means that if you wanted a zero of 50 yards for your BDC calculation purposes, this would NOT be a bore sight 50 yards right? Hence bore sighting for 50 yards thinking your good to go for using BDC would be a poor mistake.

This means that you would actually want to bore sight (which would be your first crossing) to be less than 50 yards so that the second crossing is 50 yards. Possibly 20 yards or something, depending on how much higher your scope is from your barrel.
I feel like a guy could pull out a ballistics graph here to guesstimate where it would be...


Am I on the right thinking?
Part of this is my decision if i should start investing in bore sighting components...
Should I have my second crossing at 50 yards if I want my "zero" for BDC to be 50 yards? If so, bore sighting here would be useless since it would be lined up wrong, other than getting it closer to being on paper at first to save a few .22 rounds.

FYI this particular 10/22 is actually for the GF, she is never going to pull out the BDC app and play with numbers, more just to shoot stuff and make noise, I'm hoping with the BDC she will have a easy way of lining up the cross hairs for a 50 yard shot, and then using the second circle of which ever it happens to be if shooting 100 yards, half way in between in 75, etc. Give or take. The easier it is for her to shoot, the more time i get to shoot.

As a rant, how the hell has the firearm community aloud scope ring manufacturers to just call rings "medium" or "high" or "X-high" without giving a height measurement or something standardized!!!

 

[propliner]

The boresight would need to be done at either intersect to be perfect. There would be plenty of trigonometry involved (including the scope height factor) to figure out the distance of those two crossings from the muzzle. The bullet drops in an arc from the barrel's plane and the linear scope line points down to intersect at a distance, say 100 yards.

If the distance is close it will touch the top of the parabola and the bullet will continue to fall from there. It it's further, it will intersect the arc at some point and cut through it, then touch again at the further distance. If you can figure any of those 3 points out, your bore sighting will be a success, but it all really depends first on what distance you want it to be sighted in at.

 

[Nikon Travis M.]

Over thinking it, you just want to make sure it's zeroed (on the crosshairs at the desired length) to whatever you like. Could be 84 and Spot On will make it work for the holdover. Bore sighting to me is to just get it close enough that you're not having to do 30 clicks to get zeroed. Should be in the neighbourhood, dial it in and than print out the BDC chart for and let her start blasting away. Depending how long you're shooting in my experience 50 yards would be a comfortable zero for a 10/22. Also recommend if she isn't going to play with the magnification to much that rather than printing out the whole chart, do the "expand the BDC Circles" and print out the chart the scope is most likely to be set at.