Settle a argument about bore sighting

[Bart B.]

JDGray, I think you're right. Bullets do defy gravity. Direction they travel sideways, too.

Some of them that are at the bottom of a group at short range defy gravity and move up so all of them shoot smaller groups in the vertical axis further down range.

Others on one side of that short range group change direction and head back the other way to make down range groups smaller horizontally.

Nobody's ever been able to tell how bullets know where they are relative to group center of all fired ones at some range so they change their trajectory to make them cluster closer together down range.

Surely, there's no other reason, is there?

 

[Lloyd Smale]

I wouldn't be without one. I have many rifles and more come and go and scopes are constantly swapped around and a bore slighter gets me on paper at a 100 yards and saves a lot of time.

 

[Delmar]

The only good use I have ever found for a collimator is to verify scope zero after I have done so on paper.

If I cannot see down the barrel, I make my first shot at 25 yards from a fully supported rest, then dial the scope to the hole I made. Then take it out to 100 and repeat.
What some call a field expedient zero.