Variable power scope and point of aim

[45flint]

Bought a Leaper variable power Bugbuster.  Just zeroed it in at 15 feet and then went to 50 feet and and zoomed in a bit, it was hitting a lot higher.  Thought if you focused the scope it would stay in zero at different distances and powers?

[Roadworthy]

The pellet does not travel in a flat straight line.  There is an arc of trajectory involved and actually two vertical zero points.
Download a free copy of Chairgun Pro from Hawke Optics gor a graphic representation of what's happening.

[ranchibi]

Steve, what Roadworthy said! Knowing pellet trajectory will quicken sighting scopes in in the future. When I start sighting in at close to 10 feet I want my POI to be under the target point because I know that the trajectory climbs as I move out to a certain distance then it starts dropping....what you observed.

[Novagun]

Not only that but Leapers scopes, although very good are cheaper scopes with first focal plane focus and changing the magnification changes the zero. There has been lots written about it that is accessible on the net. Don't worry, most of us get by just shooting away despite all the complications.

[GKU]

It could be defective, do a focus POI test on it.



On the BB it doesn't have a locking rear OB nut so I'd use a couple of large O-ring placed into the groove.
This will help with some of the POA issues too .......

~ GKU

[Doug Wall]

Ditto to what Roadworthy said. There is a learning curve on pellet trajectory, and zeroing at 15 ft. will certainly have you hitting high at 50 ft.. For my field target gun, I zero at about 25 yds. Closer than that, it hits low. From about 25-35 yds, it hits a little high, then after 35 yds, it just keeps going lower.

[lizzie]

Steve, what Roadworthy said! Knowing pellet trajectory will quicken sighting scopes in in the future. When I start sighting in at close to 10 feet I want my POI to be under the target point because I know that the trajectory climbs as I move out to a certain distance then it starts dropping....what you observed.

I have found that (generally), when I sight close-up (15 feet) for my initial zero'ing of a scope, I need to be about 1" under the POI, in order to be on target in the 60-70 ft range.

[Griffygriff]

(Firstly I am NOT pushing this iPhone app, just explaining why I built it  )

I noticed the same changes of POI at various distances and varying zoom levels (on a Second Focal plane) scope.  I started trying to record these settings for all my rifles (some of them had varying Power Wheel settings which also affected POI), by staying at the highest magnification and jotting them down.  But it hit me that I wasn’t using the scope’s zoom to the best capacity for each situation.

So I started taking shots at various distances and recording the MillDot offsets at different zoom settings.  This became more beneficial (for me), because after taking the shot, I would change my Zoom levels until the offset fell into clearer measurements (e.g. on the MillDot, .5 spacing between 2 MillDots etc) and also recording those. 

In the end I wrote an iPhone App called “Range Buddy” which allowed me to select rifles with varying set-ups. This allowed me to quickly roll up and down Zoom settings and see all the previously stored range offsets.  I have found that I use this app all the time now (except when shooting with the TFH guys who don’t like me looking at my phone).

[GKU]

Yes, I think what the OP is saying is that no matter what distance he zeros his BB (15-50 feet) when adjusting the focus or zoom the POI changes. For me you might need to compensate and live with (poor tracking) it like the above or just get a more quality scope like SWFA.

I would think with almost 1,000 posts under his belt he know all the above.

~ GKU

[Taso1000]

I have seen poi move at the extreme ends of the power range in two of my riflescopes.  I don't recall which scope was the first one but the last one was a BSA 2-7x.  I had zeroed at 2x and when I tested at 7x the poi moved about an inch and a half to the left at 12 yards.  I leave it at 2x and try not to use 7x.

I recently tested my Nikon Prostaff Target EFR 3-9x at both ends of the magnification on my HW100 and had zero poi change at 12 yards.

I don't know what causes it.  Probably some misalignment from loose tolerance or not perfectly optically centered lenses?

Taso

[GKU]

~ GKU

[Scotchmo]

Bought a Leaper variable power Bugbuster.  Just zeroed it in at 15 feet and then went to 50 feet and and zoomed in a bit, it was hitting a lot higher.  Thought if you focused the scope it would stay in zero at different distances and powers?

That is normal. If you zero it at a particular distance, it will stay zeroed as you change magnification. But you need to adjust your elevation or use hold over/under when shooting at distances outside your zero. That applies to any scope.

[Scotchmo]

Not only that but Leapers scopes, although very good are cheaper scopes with first focal plane focus and changing the magnification changes the zero. There has been lots written about it that is accessible on the net. Don't worry, most of us get by just shooting away despite all the complications.

Leapers scopes are second focal plane. Changing the magnification does not change the zero, it changes the subtension angle/spacing.

[rafterp]

I watched a good video on YT the other day where a guy was shooting a box with several targets on it and recording POI at 10yds, 15yds, 20yds, etc.  I did the same thing over the weekend and it is interesting to be able to see the shift. I was surprised that it did not change as drastically as I expected.
So along the same lines as someone posted above (and I'm sure this is a newbie question), I have a variable power scope, with sidewheel adjustment. However, I find that I most often shoot at the highest power (12x) and adjust focus with the sidewheel. What is the benefit of shooting at 3-4x, when you can see so much clearer at 12x?

[Scotchmo]

...What is the benefit of shooting at 3-4x, when you can see so much clearer at 12x?

Faster target acquisition. Easier tracking of moving targets. i.e. - hunting.

[Taso1000]

Exactly.  I like low power on my off hand pesting guns.  I stalk and I don't shoot beyond 20 yards. 

From a bench I like the most magnification I can get.   

Taso

[DonaAna1]

The scope is probably 1.5 to 2 inches above the bore of the rifle. At 15 ft. the projectile hasn't reached the line of bore yet. So of course your shot will be high at 50 ft.

[lefteyeshot]

Don't forget to change you AO. I zero everything at 25 yards. Guns with some power will have about the same POI at 25 or 50 yds. If I try for 100 yards with my springers I zero at 50 yds so POA and POI are at the second upper mildot. A little less hold over at 100 and it seems to keep everything closer to the center. Smaller, easier to manage.