Vernier Sights

[ColColt]

I had an interesting phenomena this afternoon. I wanted to bore sight my Browning BPCR in 45-70 so took it out on the deck and set it up steady and found an object about 75 yards away and looked down the bore and adjusted to center it. Then without moving it I flipped up the rear vernier and started elevating it since the front sight was about a foot or more low. Instead of moving up it moved it down? I ended up having to set the vernier on 0 to get the front/rear sight to agree with what I saw through the bore. That's 180 degrees from what I thought.

Seems to me raising the rear sight should have brought things up, not down. I'm still scratching my head over that one. I tried the same thing at about 25 yards away and got the same thing. It appears zeroed at 25 yard target and the other one a little further. With all the height left on the vernier it must be able to shoot over the moon.

[ColColt]

I was given the answer...

"The difference here is that the rifle is not moving, as would be the case if you were shooting. As only the sight is moving, the effect is similar to a teeter-totter, and pivoting under the front sight.

What is normal during shooting, is that the line-of-sight never ever changes. A straight line is drawn from the eyeball, through the rear sight, past the front sight, and to the target. When we "adjust sights", what we are actually doing is adjusting the gun, the line-of-sight is still unmoving. When we "raise" the rear sight, we are actually pushing the rear of the gun down. This causes the POI to raise.

During your boresighting, the rifle never moved, but the line-of-sight changed. As the rear sight was raised, the point-of-aim became lower and lower. Now that you've completed boresighting, actually sighting-in will be as you normally experience."