How common is POI shift with AO adjustment?

[vigilandy]

I  have a Nikko Stirling Mountmaster 4-12x50 mounted on my B50.  It's a very accurate gun that was formerly owned and tuned by Moorhead.   About two weeks ago I noticed the zero on the gun was off by over an inch at 35 yards.  After much frustration I figured out that the POI was shifting with AO adjustment.   The good news / bad news is that my QB79 had been suffering from the same problem which was unsolved until now.   

BOTH rifles sport the same scope.   I got a replacement for one on Friday and had a chance to shoot today. Same problem!  I set a target at 40 yards,  set the AO using head Bob method,  and zeroed the scope.  Easy 3/4 inch groups without even trying. Tiny groups are possible with this rifle,  but that wasn't the goal today.    Have I mentioned that I love this gun? 

I then changed the AO to 25 yards  and shot again.  Still tiny groups but POI shifted up and to the right about 1.5 inches.  Returning the AO to previous setting put the POI back at original location.  I then moved myself to with 25 yards of the target.  With AO still at 40 yards,  I shot high which is logical.  Then adjusted AO to 25 yards and confirmed with head bob that I was parallax free.  Pellet went even higher and off to the right again about an inch. 

This is a defective scope right?  I just find it odd that I have three of the same model with this problem and none of dozen other scopes suffer from this.  I really like these scopes but can't live with this POI shift. 

Thoughts? 

[nced]

I  have a Nikko Stirling Mountmaster 4-12x50 mounted on my B50.  It's a very accurate gun that was formerly owned and tuned by Moorhead.   About two weeks ago I noticed the zero on the gun was off by over an inch at 35 yards.  After much frustration I figured out that the POI was shifting with AO adjustment.   The good news / bad news is that my QB79 had been suffering from the same problem which was unsolved until now.   

BOTH rifles sport the same scope.   I got a replacement for one on Friday and had a chance to shoot today. Same problem!  I set a target at 40 yards,  set the AO using head Bob method,  and zeroed the scope.  Easy 3/4 inch groups without even trying. Tiny groups are possible with this rifle,  but that wasn't the goal today.    Have I mentioned that I love this gun? 

I then changed the AO to 25 yards  and shot again.  Still tiny groups but POI shifted up and to the right about 1.5 inches.  Returning the AO to previous setting put the POI back at original location.  I then moved myself to with 25 yards of the target.  With AO still at 40 yards,  I shot high which is logical.  Then adjusted AO to 25 yards and confirmed with head bob that I was parallax free.  Pellet went even higher and off to the right again about an inch. 

This is a defective scope right?  I just find it odd that I have three of the same model with this problem and none of dozen other scopes suffer from this.  I really like these scopes but can't live with this POI shift. 

Thoughts? 

I had the same problem with a 4-12x40 Hawke AirMax but my focus related poi shift was about 1 1/2" laterally when focusing and shooting from both 18 yards and 10 yards.........
Here's a scan of the target shot before even zeroing the scope..........

This scope was replaced by Hawke however the replacement scope also shifted the poi with focusing and shooting from both 18 yards and 10 yards buy not as bad........

The second AirMax was returned along with extra $$ and updated to a 4-12x40 Hawke Panorama which was actually a pretty good scope that didn't shift the poi laterally with focusing, however it wouldn't focus sharply down to 10 yards even though there was a 10 yard etching on the AO. This scope was sold to a fellow who wasn't concerned about focusing at 10 yards and I gave up on the Hawkes!

Years ago I also owned a 3-12x40 Barska that shifted the poi with focusing so it was returned to WalMart from where it was ordered.

[Motorhead]

Really not worthy to have an accurate rifle downgraded by sub par optics

[vigilandy]

Really not worthy to have an accurate rifle downgraded by sub par optics

Forgive me.....  I have offended your old rifle. 

You're right of course.  The B50 deserves better.  It is more accurate by far than anything else I've shot.  I don't have any complaints about the image quality on the Nikko,  but my experience with fancy scopes is limited to nonexistent.  However,  I can't deal with unreliability.  I am actually waiting on delivery of a Hawke Varmint 6-24X44. Hopefully my experience will be better than Ed's!   @Ed -  what did you end up replacing the Hawke with?

I've moved from from $100 rifles to $200 to $500...and now those $1000 models don't look so expensive anymore....  With scopes I'm only at the $200 - $250 stage.  This madness must stop.  I've got three kids going to preschool!   

[Motorhead]

Lol ... all said with face palm !
Completely understand the progression of rifle & optics with the ever growing hole we go down !!
Rabbit hole, hardly ... feels more sink hole to me 

[nced]

Really not worthy to have an accurate rifle downgraded by sub par optics

Forgive me.....  I have offended your old rifle. 

You're right of course.  The B50 deserves better.  It is more accurate by far than anything else I've shot.  I don't have any complaints about the image quality on the Nikko,  but my experience with fancy scopes is limited to nonexistent.  However,  I can't deal with unreliability.  I am actually waiting on delivery of a Hawke Varmint 6-24X44. Hopefully my experience will be better than Ed's!   @Ed -  what did you end up replacing the Hawke with?

I've moved from from $100 rifles to $200 to $500...and now those $1000 models don't look so expensive anymore....  With scopes I'm only at the $200 - $250 stage.  This madness must stop.  I've got three kids going to preschool!   

Ed -  what did you end up replacing the Hawke with?
Well....I used a 4-12x40 Vortex Diamondback for a couple years till I got to NC and started shooting at the THAGC club where I was shooting in the direct sun on several lanes. The Diamondback image would wash out completely due to flare through the rear lens. Matter of fact, when I attended the National field target competition in Heflin, AL a couple years ago I opted to use my cheap 4-16x40 Adventure Class Center Point since it was less susceptible to flare than the Diamondback. LOL....during the two day competition I was the sole hunter class piston shooter with my CP scoped R9 and my final score would have placed about mid way up the PCP hunter class! 

After the flareout issues with the Diamondback I bought a 3-12x50 Aeon scope and it was completely flare free even when sitting in the direct sun at a THAGC match. The issues I had with the Aeon was the fact that the reticle was rather fine with small mil dots and I would lose the reticle on the dark targets set up on a shaded lane. Also, for some reason the Aeon wouldn't "scope rangefind" adequately with my eyes and if I did a scope rangefind three times at the same target from the same position I would get three different "readings" on my side wheel.

After the Aeon I bought the 3-12x44 Optisan Viper that I'm currently using! It's been the best scope I've owned for hunter class field target shooting since it readily snaps in and out of focus when scope rangefinding, it has an illuminated reticle if needed for aiming at dark targets on dark lanes, and the optics are very good allowing me to easily see .177 pellet holes in paper targets! The only issues I have with the Viper is the "brick like" size and weight on the receiver and the hokey way the large sidewheel is mounted to the focus knob. The factory setup uses only three set screws compressing a rubber hub to secure the large focus wheel to the knob. This gives a less than solid mounting to the wheel. I solved the issue with my scope by drilling and tapping four mounting screw holes in the sidewheel and securing the wheel with nylon tipped set screws. I also machined a rim to cover the sw "knobbies" so I had a larger flat surface for mounting my holdover tape. Here are a couple pics.
Viper with trimmed sun shade on the HW95.........

The factory large focus knob..........

The ring on the sidewheel was too large to fit between the rings of a UTG one piece mount.........


The solution, machine away the "offending ring" and make a press on rim from an ABS plumbing fitting to give a "holdover tape" mounting surface........

Final result.........




As a side note...........
For mounting the scope in a one piece BKL mount there was no need to modify the large sw that came with the Viper because there was more distance between the rings. The issue I have with the BKL mount is that it's difficult to keep the scope and mounts from sliding even though my HW95 is tuned to less than 14fpe!

The mount sliding on the receiver was "fixed" by torquing the base screws to 35 inch pounds and the only way I could keep the scope in place was to line the rings with some electrical friction tape.

Because of this I opted to machine the large focus wheel and use a cheap UTG one piece mount with a stop pin.
   

[robertr]

 Andy, I hope you get a good Varmint Scope, I just sent my Varmint back on warranty.

[nervoustrigger]

I am actually waiting on delivery of a Hawke Varmint 6-24X44.

Shoulda got the BSA 6-24x44 and pocketed the difference

Better glass than any Varmint or Sidewinder I've ever used, just not made for springer thrashing, and the fine etched reticle makes precision aiming at a distance really easy.  I didn't see the reticle construction on the Varmint but I assume it's wire since it didn't say etched.

[condor22]

Really not worthy to have an accurate rifle downgraded by sub par optics

 + 1   

[vigilandy]

Thanks for the detailed response Ed.  I will have to take a look at the Optisan Viper.  I'm guessing it's a little out of my current price range... but that is pretty glowing review from you!

@Nervoustrigger-- I've got one of those BSA scopes courtesy of your last recommendation Jason!   It's nice and I would've got another, but the turrets are exposed and non-locking! 

@robertr-- I really hope this Hawke works out.  I've had a bad run.  Two of the Nikko Stirling Mountmaster scopes, two BSA (Contender and Target), and a Bushnell Trophy (6-18x50 AO) to return.  Did your Hawke suffer from shifting POI when you adjust the AO?

@condor22-- You don't have to say anymore.  Cheap scopes have come back to bite me.  Other people seem to have better luck.  Or it could be that I have lots of cheap scopes and cheap guns.   

[robertr]

 Your not alone Andy, I am on my 4th Hawke, two EV's, one Varmit both models had factory defects. Distributer said the Varmint scopes are very popular and all of a sudden he had 20 Varmints returned with the same problem, mine never held zero and finally the reticle turned counterclockwise. I think he said the Varmints are being replaced with the Vantage line. So now I wait for the Airmax 30 to arrive, way more scope than I originally wanted, as long as it works.

[nervoustrigger]

Hi Andy, understood on the BSA turrets.  That concerned me too when I first got it but it hasn't been a problem even once so I had forgotten about it.  Has it tripped you up?

[vigilandy]

Hi Andy, understood on the BSA turrets.  That concerned me too when I first got it but it hasn't been a problem even once so I had forgotten about it.  Has it tripped you up?

No problems yet, but this Varmint was originally meant for a new rifle for my dad- a rifle that gets stashed haphazardly at times (truck gun in the full sense of the phrase). I also have a Leapers SWAT coming too (exposed,  but lockable turrets).  He's not getting his new toy till his bday in October so I have time to order him another scope.  My wallet isn't going to like it though. I don't want to end up like robertr-- I'd to keep my scope expenditures from creeping up! 

What I really wanted on the B50 was the Bushnell Trophy XLT 6-18X50.  Not sure when I will get it replaced though. 

[Methuselah]

I set a target at 40 yards,  set the AO using head Bob method,  and zeroed the scope.  Easy 3/4 inch groups without even trying. Tiny groups are possible with this rifle,  but that wasn't the goal today.    Have I mentioned that I love this gun? 

I then changed the AO to 25 yards  and shot again.  Still tiny groups but POI shifted up and to the right about 1.5 inches.  Returning the AO to previous setting put the POI back at original location.  I then moved myself to with 25 yards of the target.  With AO still at 40 yards,  I shot high which is logical.  Then adjusted AO to 25 yards and confirmed with head bob that I was parallax free.  Pellet went even higher and off to the right again about an inch.

 

Not convinced it's the scope.

1)  "I set a target at 40 yards,  set the AO using head Bob method,  and zeroed the scope."

40 yard zero, check.

2)  "I then changed the AO to 25 yards  and shot again.  Still tiny groups but POI shifted up and to the right about 1.5 inches"

Not relevant, you now have parallax adjustment off and POA and POI won't track unless you have perfect cheek weld positioning

3)  "Returning the AO to previous setting put the POI back at original location"

Rightly so!  So changing the scope settings isn't necessarily causing an issue with the mechanicals in the scope (good!)

4)  "moved myself to with 25 yards of the target.  With AO still at 40 yards,  I shot high which is logical"

Trajectory changes with distance, but, not relevant for same reason #2 - you just lost your ability to compensate parallax again

5)  "Then adjusted AO to 25 yards and confirmed with head bob that I was parallax free.  Pellet went even higher and off to the right again about an inch."

Left to right is potentially scope cant.  Try putting a level on the rail and sighting in on a plumb line, see if the scope is rotated...

Just my $.02

[sscoyote]

This is one of the reasons a grid boresighter can be your best friend. It'll tell you very quickly without even firing a shot if your reticle is shifting. I'm sending an optic back as we speak due to this very problem--only this one jumps all over the grid about 4 MOA with a power change.

[robertr]

This is one of the reasons a grid boresighter can be your best friend. It'll tell you very quickly without even firing a shot if your reticle is shifting. I'm sending an optic back as we speak due to this very problem--only this one jumps all over the grid about 4 MOA with a power change.

I agree, for the amount of money they cost they are very handy. Also good when barrel bending.

[vigilandy]

Thanks for all the input.  I've just tried the same experiment with a Leapers 4-16x44.   I get some POI shift,  but only as can be expected (up and down) when varying distance.   The Nikko Stirling POI shift was further than the POI shift (as tested using head bob). 

As for scope cant,  that is possible, but I think the can't would be noticeable considering how far off the POI was from the POA.  At this point I'm thinking some pictures would be useful huh? 

I had never heard of a "grid bore sighter"  until just now.  What an awesome tool.   Considering how often I play musical scopes with my guns,  I NEED one! 

[Geoff]

This is one of the reasons a grid boresighter can be your best friend. It'll tell you very quickly without even firing a shot if your reticle is shifting. I'm sending an optic back as we speak due to this very problem--only this one jumps all over the grid about 4 MOA with a power change.

I like gadgets so just may get one to have in the kit, however pellets are cheap and I start the test in the basement at 5 yards, move outside to 15 yards then to my final spot at 20-28 yards.   I leaned to not take the 5 yard as a sure thing so do it in steps.

Like I said, I like gadgets so will probably get one and it will sit next to the 2 pellet sizers I own that I really never use.  LOL

[Methuselah]

Thanks for all the input.  I've just tried the same experiment with a Leapers 4-16x44.   I get some POI shift,  but only as can be expected (up and down) when varying distance.   The Nikko Stirling POI shift was further than the POI shift (as tested using head bob). 

As for scope cant,  that is possible, but I think the can't would be noticeable considering how far off the POI was from the POA.  At this point I'm thinking some pictures would be useful huh? 

I had never heard of a "grid bore sighter"  until just now.  What an awesome tool.   Considering how often I play musical scopes with my guns,  I NEED one!

Cant effects left to right, distance only up & down in still winds.  Cant can be checked for but remounting the scope means it may not be there anymore ... zero closer, say 20.  If for example it shoots left at 10, right at 35, that's cant (ignoring up/down).  Don't zero 40 for this check cause of wind...

Also, see you repeated experiment, if you head bob, POA is you, but change range or twist AO and you MUST head bob again or else you won't be sure if POI shift is you, or paralax!

Grid thing can be done by securing gun from ALL movement and watching POA at different power setting(s), no?

Hope you get it ironed out 

[sscoyote]

My Bushnell magnetic grid BS'r is the handiest gizmo I have. I use it for--

1) Rough zeroing at home
2) Setting up my scopes/rings for long-range
3) Some reticle subtension calcs
4) Checking reticle shift with power/parallax changes
5) Repeatability/consistency of turret clicks.