Scope zero - one distance only

[tworst]

I am trying to figure out how to zero my scope in a particular way.  Its easy just to pick out some arbitrary distance, shoot, adjust the turrets and have it zeroed at that distance.  However, it is almost inevitable that it is also zeroed at a second distance as well, either before or after the first distance.  This is because the barrel must be angled up slightly relative to the LOS of the scope to get the pellet path to intersect with the scope LOS at some distance.  But it would seem almost impossible to have it intersect at only one point because of the arc of the pellet.  If you could get one point intersection, then you would always hold over at every distance before and after the zero point.

It may be helpful to think in terms of a laser instead of a scope.  Just a device mounted on top the rifle that puts out a straight beam of light at some angle relative to the longitudinal axis of the barrel.  The laser has no optics, reticule, turret, or adjustments of any kind.  The only way to change the angle is to shim the mounts.  It should be easy to see that the laser could be shimmed in such a way so that it intersects with the pellet arc at 2 points, 1 point or 0 points, depending on the angle.  Getting it to intersect at only one point could take quite a bit of tweaking.

A scope functions in fundamentally the same way.  Although, it may be more complex because I don't exactly know how the turret adjustment effects the LOS of the scope.  I suspect that the LOS of the scope is fixed by its mounting orientation.  Adjusting the elevation turret just adjusts the aiming point of the reticle.  Since this is a "point", it doesn't actually change the "LINE" of sight of the optics of the scope.  So it would seem that the only way to get a single point of intersection would be to shim the scope.  In addition, the distance at which the single intersection occurred would be fixed by the barrel and scope mounting relationship and the ballistics of the pellet and could not be changed by adjusting the turret.  Now, if adjusting the turret actually changes the real lengthwise angle orientation of the optics body inside the tube, not just a point on the reticle, that would be the same as shimming the entire scope body and thus the real optical LOS.

I think its probably easiest just to zero in your scope at a desired distance and then field test other distances to see where you have to hold over and where to hold under.  It is just an interesting concept to me to be able to get a single point intersection zero at a desired distance, just don't know how it would be done or even practical.

[Bullit]

You might be enlightened by looking in Pyramid Air website.  They have a section of videos titled "Airgun Academy". 

I am not a fan of a single point zero, because the flight arc is small (within reasonable ranges), and can easily be contained within a 1/2"  killzone.  This gives you more "effective range" flexibility without a lot of head scratching.
Download the program "Chairgun Pro".   It will educate you and illustrate everything you wanna try, with good graphics and understandable data tables.   Spend some hours playing with it and you'll see how beneficial it can be...even just for brainstorming    

[starlingassassin]

if you zero at the very top of the arc of the pellet trajectory then you will have only 1 zero distance

[cactusrat]

If I hear what you are saying, you want to be able to “hold over” at all distances, except for what the gun is zero at.

If this is right, then it’s not going to happen.

If you sight in at 150 yards ( first zero will be something like 1 or 2 yards depending on the fps of the gun), everything from 5 (depending on gun) yards all the way to 150 yards you will have to use “hold under” to bring the pellet flight “down” to hit a target.

A pellet starts falling as soon as it leaves the barrel, that is why scopes have to be angled down (the line of sight ) slightly to cross the pellet’s path.

If the scope can be mounted even with the bore (not above, like on top of the gun as they are) then the path of the pellet will stay below the scope’s line of sight and you could hold over to make all shots.

[rsterne]

A one-point zero is easy to do, it's only a few clicks less elevation than a conventional two-point zero.... I always use a two-point zero for hunting, with a 1/4" rise between, to give me the longest possible 1/2" kill zone.... I understand that for serious FT work the one-point zero is preferred to avoid confusion, as you NEVER have to worry about hold-under on really small KZ's.... just range and click UP from your zero point....

Bob

[rsterne]

Getting it to intersect at only one point could take quite a bit of tweaking.

HUH?.... less "tweaking" from parallel to the bore than to intersect at two points....

you want to be able to “hold over” at all distances, except for what the gun is zero at.
If this is right, then it’s not going to happen.

Again, HUH?.... If the scope is zeroed to the top of the pellet arc (relative to the line of sight), then you will never have to hold under....

Bob

[Bullit]

I don't know what caliber, or rifle you are using, but if you lay 2 .177 pellets together, they'll measure just less than 3/8 wide"

Heck, unless you're a super breather steady shooter, you'll be shooting in a 1/2" window (killzone/KZ) on your better days. With 2 zero system, you know what that window of error is as well.

[tworst]

I have a FX Whisper .22, shooting 15.9 JSB, around 850 ft/sec muzzle velocity, Hawke 4x12 40 mil dot scope.  I am just experimenting with how to set everything up and I am not exactly sure what I want at this point.  On thinking it through, it just occurred to me that getting a single point zero might be difficult.  Not sure it would even be desirable. I am just trying to understand everything more than anything else. 

I did download Chairgun.  How do you turn off the .177 POI on the graph?  The box seems greyed out.  I just want to see my own gun/cal without .177 info at the same time.  Also, when I go to pick a pellet profile, it only lists .177 cal, nothing in .22.

[Bullit]

Glad the light turned on...
With Chairgun Pro,  It will take you a little playing with to fully learn,  and enjoy the program.   
You can manually enter whatever you want in each block at the top and it'll calculate for your entries.   It'll warn you of invalid entries.   For "calibre", just right click it and select.  But again, you can do all the block entries manually.   You need to scroll down in the "pellet database" menu, and you'll find that it has many caliber pellets listed, with all the data.  Edit:  For a list of the most popular pellets in use, just Click on "FILE"  then select "Pellet Database".
Don't get in a hurry.    Spend some time, and you'll learn with it.

[rsterne]

tworst.... For your velocity and pellet, try a 23.6 yard zero.... That will give you a one-point zero, assuming your scope is 1.5" above the boreline....

Bob

[cactusrat]

In Chair gun, click on the tab at the very top  that is labeled .22 cal ( I think it’s the third from the left). When you are in the 22 caliber tab, click on the pellet name under the first tab. That will bring up the 22 caliber pellet data base.

Click the pellet you want to use and then fill in your muzzle velocity, scope height and the power of the scope that you be shooting at.

With this basic data, you should be able to figure out the rest to get started. As you learn Chaingun better, then other variables can be changed.

[rsterne]

Just learned a trick on ChairGun.... If you set the "Kill Zone" to 0.000, and then right click on "Zero Range" and select "Optimize OZR" from the drop-down menu, you will get a one-point zero....

Bob

[Bullit]

Use the "Zenith" feature and it will gets you there for 1 point.
I use this, because it's quick reverting back to a previous setting.  I'm using an older version, Bob, so maybe it toggles better with newer versions.

[tworst]

Thanks for all the tips guys.  Amazingly, I filled out all my gun info and was already very close to a single point zero with scope at 1.75 height, 800 ft/sec and zero at 25 yards.  After looking at the graphs, it looks like I could re-zero at around 35 yards and have a +/- 0,5 inch kill zone from about 10 to 42 yards with two zeros.  This is probably just fine for hunting. For target shooting, learning my gun, scope, mil dots, etc., I think I will just leave it zeroed at 25 yards and continue learning.

[puttster]

First post here.  I bought a Gamo Hornet to kill the doves roosting in a tree next door.  It will be about a 25 yard, 45 degree shot.   I have been zeroing the gun, to zero to a single point at 25 yards.  At first it seems like a bad idea because in  practice my shots would tend to group below the target if the range was any different than 25 yards.  But when I switch to a 45 degree angle, maybe the kill zone will rise up.  Am I thinking right about that?
putts

[chiro972b]

First post here.  I bought a Gamo Hornet to kill the doves roosting in a tree next door.  It will be about a 25 yard, 45 degree shot.   I have been zeroing the gun, to zero to a single point at 25 yards.  At first it seems like a bad idea because in  practice my shots would tend to group below the target if the range was any different than 25 yards.  But when I switch to a 45 degree angle, maybe the kill zone will rise up.  Am I thinking right about that?
putts

If I'm understanding what you're asking then yes, as you angle the barrel upwards, your poi will rise in reference to your zero so that you may even need to hold under. Also be aware that the arc on most guns is shallow enough on most guns that if you zero at 25 yards, when shooting level, you will be close enough to the kill zone if you aim right at your target from around 20-30 yards or even a bit more.