Wandering Zero

[danfick]

Hi All

I purchased a new (preowned) Hawke scope for my BSA Ultra. The rifle itself has been shooting some fantastic groups with an old Nikko Mountmaster I threw on it when I purchased it. I have put the Hawke on the rifle and once zeroed I have been shooting groups but it seems that the gun won't group. (Think 1"-1.5" instead of the .25" groups when rested at 25 yards). Initially I was thinking pellet but tried some different pellets. Then looked at my shooting but I have ruled that out with my AAS410 .22 and the groups are nice and tight with that. I then went to scope.

Looking through it it is really clear, the turrets seem to move the crosshair appropriately and accurately when the rifle is held securely and there is no looseness to anything on it, nor is anything rattling (unlike the Nikko that does). I put the old Nikko back on the rifle and it's shooting great tiny little groups again, I didn't even have to rezero. After eliminating everything to this point I tried shooting the new scope again with a lower magnification setting as the Nikko maxes out at 9 but still haven't had any luck.

Does anyone have any idea what could be causing this? I have checked the screws are not over tight (have used a torque screwdriver at about 1.25 ft/lbs, which appears to be the recommended tightness).

Thanks for your help

Dan

[TORNADOS7]

What scope is it, is it PX adjustable or PX'd at the rite distance (35yds should do it) being second hand I'd be inclined to say it's knackered, could it possibly have been on a springer at some point ?...

[NewPaul]

From what you say, it does point towards a dodgy scope.

[Scubashot]

A lot of the older budget scopes that have adjustable objective lenses an/or zoom will shift their point of impact if you rotate one of the lenses.
Because they are not optically perfect the image in the lens (which is what you are actually aiming at) is not dead in the mechanical centre of the scope and moves as you rotate the lens.
The more expensive side focus arrangement effectively eliminates this problem.
I also have a Nikko Mountmaster AO that changes its point of impact by three inches just by changing the AO setting from 25 to 40 yards!

[danfick]

The scope is a 4-16x50 AO Mildot and the problems occur without me adjusting the magnification. The AO adjustment is correct to my target, this was set before zeroing. I am thinking knackered scope too

[lensman57]

Focus shift is the only culprit that I can think of .

A.G

[Unframed Dave]

Is the reticle the same thickness?

Dave

[danfick]

No, the Nikko has a thicker reticule which isn't as nice to shoot with

[angrybear]

Have you tried altering the eye relief & playing with the ocular focus ? some scopes are way more critical on having your eye central where others are more forgiving (ie the picture still looks round & central even though your eye is off centre)

You say the AO is correct to your target - ignore the range numbers, the odds on them matching your eye are slim to none, adjust the focus to suit your eye which you'll probably only notice above 10x mag.

But to go from 1/4" to 1.5" it sounds like the scope is duff.

[TORNADOS7]

Remove the scope from the rifle/mounts, remove the turret caps and anything else that may make a noise then bring it up next to yer ear and give it a firm shake, if you can hear a faint 'kerchink kerchink' emanating from inside then the scopes a gonner !...

A little issue I like to refer to as 'springer syndrome' where the internal lenses have been rattled loose by the bi-lateral recoil of a spring powered gun, I know it well, it's cost me a f***in fortune over the years...