Scope issue: When I turn the knob "up', shouldn't POI move "UP"?


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Buckskinner
March 8, 2003, 02:40 PM
So I wanted to know more about my new Bushnell Elite 3200. Its sighted in dead on at 100 yds, and I wanted to know if I was close to mechanical zero. I put the laser bore sigher in the muzzle, placed the rifle in a rest and set up the target across the kitchen. Following the laser bore sighter directions, the cross hairs were higher than the laser light. I then dialed the scope "UP" 147 clicks. Looking through the scope, I saw the scope's cross hairs well BELOW the laser light. Shouldn't this be the opposite? Is there something wrong with my logic, or the scope?...:confused:

I didn't try windage.

The scope is mounted on an old style Ruger m77 in '06, on medium rings.

By the way, it was 147 up and 168 down...

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Keith
March 8, 2003, 02:57 PM
Throw your laser bore sighter away.

Put your rifle in a vice or firmly in some sandbags and just look down the bore and center a small object at least 100 yards away. I have a streetlight out my kitchen window that works for me.

When you get the object firmly centered in the barrel simply twist the knobs until the scope cross-hairs center the same object - looking through the barrel and through the scope in turn.

I've bore sighted many hundreds of rifles with various types of bore sighters and found that this kitchen window method is far more accurate and faster as well.

The problem (I think) with these various devices is that they are working on target only a few feet away, or even at the end of the barrel. It may be a parallax problem or something.. I don't know. I do know that when I use the kitchen window method and then go to the range, my bullets land within inches of the bullseye. When I use bore-sighters I'm lucky if they are on the paper.

Keith

TallPine
March 8, 2003, 03:27 PM
This always gets me confused too. I get it all figured out and then the next time I sight in a rifle, I have forgotten which way it is.

Basically, though, your rifle with any given ammo will hit at a certain spot (within the accuracy of rifle/ammo combo) relative to the barrel. That point is fixed - you can't change it.

What you can change is your aiming point. So if your rifle shoots LOW, then you need to bring your aiming point DOWN to where the the bullet actually hits. By doing this, you apparently move the impact point of the bullet UP, which is usually how the scopes are labeled.

===
As far as bore sighters, they can work pretty good. I used to work at a hardware store that also sold guns. So I used their bore sighter (the kind with the funny little target grid held up over the muzzle). Always wondered how they turned out, then a guy came back in and said it was right on windage and 2 inches high (or low?) at 100 yds. Wow, bullet weight could account for that.

Another guy bought a rifle and scope, then hurt his hand and couldn't sight it in. So his wife goes out and kills a deer with this unfired rifle. :eek: It must have been pretty close, at least the deer didn't complain about it. :)

Buckskinner
March 8, 2003, 03:32 PM
I appreciate the time you took to respond, but, the issue is not the bore sighter.

Using the relationship between the bore sighter laser and the scope's cross hairs as a reference, shouldn't the crosshairs move UP, away from the muzzle's straight line, when dialing the scope UP? The opposite is happening with my rifle and scope.

TallPine
March 8, 2003, 03:38 PM
BuckSkinner:

Read the first half of my post again.

Your scope is working exactly right.

If you were to move the crosshairs up relative to the barrel, your rifle would shoot low.

Just remember that you are changing the aiming point, not the impact point.

Buckskinner
March 8, 2003, 04:17 PM
Sorry, I'm not getting it. Is it really that counter-intuitive?

Let's say I'm literally "bore sighting the rifle", using Keith's method (which I often use at the range) of removing bolt and sighting through the bore at the target, then dialing in scope for same. When I want to move the cross hairs UP, because i want my point of impact to go up, I should dial the windage knob on the scope in the direction that says "UP", right? Well when I do this, the crosshairs move down, moving the POI down. That seems wrong to me!

What am I missing?

Al Thompson
March 8, 2003, 04:25 PM
I think this someething that could be shown in a couple of seconds, but on the net, tis a difficult thing.

UP = bullet up. Reticle down.

Keith
March 8, 2003, 04:37 PM
>>>>When I want to move the cross hairs UP, because i want my point of impact to go up,<<<<

Just think about that.

You are not moving the point of impact, you are moving the cross hairs to intersect the point of impact. See what I mean?

You can't move the point of impact!

So, your scope adjustment is doing exactly what it is supposed to do.

As for the laser vs field bore sighting - think about that as well. The laser method works exactly the same as "eyeballing" the bore. You are shining a laser light out of the bore and then adjusting your scope to intersect the beam of light. The difference is that beam of light is only a few feet away while "eyeballing" the bore at the range allows you to use a target 100 yards away, or further.

See? Using the longer range has to be more accurate.

Keith

DMK
March 8, 2003, 04:50 PM
You can't move the point of impact! That is a profound statement Keith.

You never really think about it this way, but at a given range, the rifle will always put the bullet in the same spot, more or less.

What we do is move our crosshairs towards where the bullets are already hitting.

When sighting, we bring Point Of Aim(the crosshairs if you will) to the Point Of Impact so they may coincide at the same spot at a given range.

If the bullets hit low, in reality we are aiming too high. To correct, we turn the screw marked "up", but the crosshairs move down to where the bullet holes are. Then when we put the crosshairs on target, it points the rifle a little higher. When we shoot and wadaya know! The bullets appear to hit higher.

Keith
March 8, 2003, 05:00 PM
>>>>When sighting, we bring Point Of Aim(the crosshairs if you will) to the Point Of Impact so they may coincide at the same spot at a given range.<<<<

I think you've articulated that better than I did.

Keith

Buckskinner
March 8, 2003, 05:25 PM
Thanks for holding my hand through this. The "Ahah!" moment was more like "oh. imadum****..."

I understand now. If the plane of the laser stays constant, then the plane of the bore moves up.

In other words, when I turn the dial that says UP, its moving the relationship that results in POI up, up. Backwards, this means raising the bore up...

Anyway, I've been shooting round balls, and fixed buckhorn sites for too long...

Thanks all..

BigG
March 8, 2003, 07:39 PM
Think of it this way, Buckskinner, with your sight line canted about a couple feet below the bore axis your gun should be point blank for about 1500 yards or so.

Buckskinner
March 8, 2003, 07:44 PM
That's just about right for lobbing 'em in there!

curt
March 8, 2003, 08:27 PM
Maybe i'm just challenged but i've had optics that when you moved the adjustment in the up (or right for that matter) on one scope from one manufacturer it would move in one direction and on others it would move in another. I always just fire a couple move the adjust 2 or 4 clicks to see if things are moving where i want them and then fire a group and start adding in clicks as necessary. sometimes the controls can stick (tho they shouldn't on a good scope) and a tap with an appropriate object after adustement can help.

I agree with keiths method. I've also used it when barreling FALs and ARs to ensure my windage was right, works every time.

JohnBT
March 8, 2003, 10:20 PM
Right. Visualize it...

Turn knob UP...crosshairs go down.

Now, to get the crosshairs back on target you have to lift the entire gun UP...and the barrel is now pointing higher.

John

P.S. - Unless you're left handed and mount your scopes with the UP knob pointed left and the windage knob pointing up. Then the U-D knob is windage and the L-R knob is vertical. :)

Al Thompson
March 8, 2003, 10:36 PM
If you really want to see someone's eyebrows go up, offer to one shot zero the rifle. :what:

You have to have a vise or good rest/bag set up and a buddy. Get the rifle bore sighted (Keith's method has worked the best for me), get in a good tight position and fire the rifle. If the bullet strikes paper, your in business. Best to have the scope caps off. Resettle the rifle in the bags or if you have a vise, now's the time to use it. Align the crosshairs just like they were when you fired the rifle. Hold it tight (!!) and have your buddy turn the W/E knobs to move the crosshairs to the bullet hole. I find that one at a time works best, and don't confuse him with "up or down" - just get him started and let him know if he's turning in the right direction.

Works well, but I always like to confirm with a group.:D

yzguy
March 10, 2003, 12:32 PM
true you are changing the point of aim, but the directional markings are for point of impact. What that means is that if you shoot at a target 100 yards away and shoot low, you would turn the dial on the scope in the "Up" direction. This moves the POI up, kinda. It really moves the point of aim down, you don't change where the bullet goes, only where you are looking. The markings are made to be clearer while trying to sight in at the range. "Up" actually moves the cross hares down. So when bore sighting you must do the opposite direction to get the desired change for both windage and elevation.

That is, if you center the bore on an object, and the scope is aimed above it, you would turn the knob in the up direction to move the cross hairs down to match where the barrel is pointing.

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