Unexpected zeroing problem

[Portzy]

I just wondered, is it possible to confuse the 1st and 2nd pbr's? Thats to say you are looking for the second but somehow you are mistakenly adjusting towards the first.

The ingredients are; a 4.5 x14 50mm Hawke scope sat atop a .22 BSA Lightning using JSB Express over 25 yards, the scope has been neither optically or mechanically centred prior, (maybe i should have?). This evening, while zeroing, I ran out of elevation while the POI was still some 2" or so below centre so this set me to thinking that the pellet was still on the rise.

Is this possible or is the scope a duffer maybe.

Thank you.

[tinbum]

Shim the back of the scope.

[angrybear]

To be out that far either duff mounts or duff scope.

Unless the barrel's pointing down.

[secretagentmole]

Bad scope rails?
It is a BSA Lightning.....

[adiepie]

1) reverse the mounts (front to back)

2) Invert the mounts (left to right)

3) reverse again

How much does the POI shift?

Also, a gentle thwack on the scope (use the heel of your shoe) between adjustments sometimes shifts a sticking erector mechanism?

Adrian

[series2a]

Had same problem it was a non matched set of mounts, try a set you know that were a real pair and try again.

[Portzy]

Thanks folks. Yes, it's on a Lightning minus the riser thingy but with a one piece Sportmatch mount. Presently it's fitted with the clamp bolts facing left, (as you look down the rifle from the rear), so I'll srip it down today, spin it round, and see how things go.

[averageplinker]

Could it be the breech seal is protruding too much making the barrel point down a smidge?

[secretagentmole]

Thanks folks. Yes, it's on a Lightning minus the riser thingy but with a one piece Sportmatch mount. Presently it's fitted with the clamp bolts facing left, (as you look down the rifle from the rear), so I'll srip it down today, spin it round, and see how things go.

If necessary shim using strips of plastic cut from a drink bottle. Centre the scope adjusters, put 2 in the back mount, tighten and start again!

[RobF]

At close range the adjustment is trying to defeat the distance between the bore and the centre of your scope, which if you're using a 50mm then it's at least 25mm, probably more.

It's not unusual to run out of adjustment if you're mounts are high and your target range is close in, or far away.

I'd advise against shimming, it's a cheap fudge that stresses your scope by bending it slightly. If swapping mounts around doesn't solve it, then a set of adjustables is the best solution.

[secretagentmole]

At close range the adjustment is trying to defeat the distance between the bore and the centre of your scope, which if you're using a 50mm then it's at least 25mm, probably more.

It's not unusual to run out of adjustment if you're mounts are high and your target range is close in, or far away.

I'd advise against shimming, it's a cheap fudge that stresses your scope by bending it slightly. If swapping mounts around doesn't solve it, then a set of adjustables is the best solution.

And using a set of adjustable mounts will put in as much flex as using a shim, you have to raise the rear mount, so shimming us just is viable an option!

[RobF]

And using a set of adjustable mounts will put in as much flex as using a shim, you have to raise the rear mount, so shimming us just is viable an option!

No it won't.


Shims mean the rear mount surface is level but at a different height to the front mount forcing the tube to bend in between.

Adjustables mounts are articulated and the top half can turn to align to the angle of the tube as more elevation is given to them meaning the scope tube is angled but kept straight across the two mounts. That's why they were invented.


So to reiterate, shimming is a fudge that puts stress into the scope by bending it, adjustables don't.

[secretagentmole]

No it won't.


Shims mean the rear mount surface is level but at a different height to the front mount forcing the tube to bend in between.

Adjustables mounts are articulated and the top half can turn to align to the angle of the tube as more elevation is given to them meaning the scope tube is angled but kept straight across the two mounts. That's why they were invented.


So to reiterate, shimming is a fudge that puts stress into the scope by bending it, adjustables don't.

Just how tight do you do up your scope clamps? Shimming works, does not bend tubes if a modicum of common sense is used.

[rancidtom]

Soft shims used correctly will not bend a scope tube, hard shims will unless the screws are left too slack to gip the scope properly and seeing as this is a recoiling rifle it can cause crimping and bending to the scope tube if done tight enough to prevent the scope moving in the mounts.
I stroungly suspect a barrel misalignment problem or quite possibly the rear of the mount has been fitted OVER the recoil arrestor stop thus not allowingg it to clamp correctly on the scope rails. A one piece mount will need to be mounted in front of the arrestor stop.

[NigelG]

Have you got a long straight edge, you can use a length of string pulled tight. lay rifle down and place straight edge along centre of barrel. If it starts to work its way to the top of the action, your barrel is drooping. In a gun shop years ago and a dad and son came in and complained they could zero it. The droop was so obvious just by being further away from it and looking at it