Scope Zero Question?

[whiteleggHW77K]

Finally getting round to fine tuning my zero.

Accuracy was good at 10yrdsish and I though good at 25 yrds (zero).
However when I got round to regularly putting 10 pellets into the same target, I started to see some trends.
At 10 yrds it was hitting consistently 1cm to the right.
And at 25 yrds it was hitting 1/2 inch low and a 1/2 inch to the left.
Figure approximate.

Obviously this cannot be cured by twiddling the knobs....so another solution has to be found.
But what is the likely cause.

Tonight I tried centering the adjustment knobs to start again.
Then slackened of the scope rail clamps and retightend.
Couple of shots at 10yrds an inch left.

Tried slackening off the scope clamps. Then with the rifle supported on two tripods I adjusted the tripods so the reticul was centred on a spot on the target.
When I rotated the scope back and forth, the reticule traced a smile on the target. see mouth left!
Should this happem, or is this a symptom of my problem?
Do I need to shim something, and do I shim inside the rings or between the mounts and the dovetail?

It is an HW77k with two piece four bolt mounts, (so thats 16 bolts in all!)

I'd love to sort this out, 'cause then I can sort out MY technique, and work on getting my zero moved out to 30 then 35 yrds. (The back fence and OH's reluctance to have me firing from the middle of the lounge, prevents a longer zero )

Thanks in advance for any responses.

Pete

[swedey21]

Sounds to me like you scope isnt level with the bore.
how did you mount the scope?
i use a plum line and a spirit level..

[Bales1983]

Im o expert but from what ive read on here in the past your reticle needs adjusting mate,

Shouldnt make a smiley while twisting,

The centre should remain centre all the time.

How to adjust i i do not know but someone here will

Lee

[Murphy]

Lost me!!

[Gwylan]

If the scope isn't exactly optically centred, (and most aren't,) when you rotate the scope in the rings, you will get a "smiley." This doesn't mean there's anything wrong. Do a search on "optically centreing your scope."
If you're only an inch out, I don't see how you can't "twiddle the knobs."
If its a .177, zero at 15 yards, then it should be close at 35, so fine tune at 35 yds. If its a .22, make it 30yds.

Gus

[whiteleggHW77K]

I could just twiddle the knobs...BUT..because it's off to the right at 10yrds and off to the left at 25yrds, I can fix one but not both by zeroing with the turrets.

Optical centering was the way I was thinking of going, Just didn't want to waste my time doing something unnecessary.

With regards to getting the scope level, I have various vertical bits of string and rope round the garden, courtisy of my kids, which tells me when the reticule is vertical....however I haven't quite managed to work out when the rifle is vertical/horizontal, also do I need to worry about the front to back level, and if so do I do this with the scope out....it's a 50mm so the front is taller than the back, so I can't put a level along it.

If anyone has optically centred their scope, I guess by shims (film neg or bits of metal. I am still unsure wether to shim the rings, and risk putting stress on the scope tube, or to shim the dovetails......


Time for bed now.
Hope to pick this up again at 05:00

Pete

[steveggg]

Pete,

Normally, on 1 of the mounts, there is a grub screw that can be wound out 2 locate into 1 of the holes, or a fixed pin.
Most people use a single mount on springers, as they are more secure if the gun has a kick, usually only tuned guns will take two piece mounts, and as a last resort DAMPA mounts are also used.
Can you tell us what mounts and scope you have.

Steve

[whiteleggHW77K]

The scope is a JSR 6-24x50 from Perry190, the mounts are no-name (I don't know it) two piece double clamp high mounts that perry sent with the scope.. by the look of the lovely website, they look like Accushot ones.

CHECK OUT THE WEBSITE.....NEW SCOPES NEW SCOPES

I think I may have spotted the problem, as I put my rifle away this morning.
I have the scope mounted quite far back, and have put the mounts as far apart as possible....this means that the rear mount was on the end piece of the receiver......the one you unscrew at 20 paces distance incase it launches at your head

On close inspection, it looks like I have quite screwed it back on completely.
So the bevel on that piece is slightly out of allignment with the longer bevel on the rest of the rifle.

I shall move the scope clamp forwards tonight and see if this solves the problem.....if not I shall try tuning one round, then the other, then swap them over etc etc etc...anything to avoid shimming!!!

Pete

[Gwylan]

Pete... in your first post, you implied that your scope was zeroed at 25yards, then you said it was shooting right at 25 yards, so your zero has shifted in some way. Have you got a rifle like the S400, where a knock on the muzzle can shift barrell alignment?

Gus

[whiteleggHW77K]

Good point.
Yes it has been knocked in the past, but I thought I had corrected that.

When I said previously it was zero'd at 25yrds.....I thought it was.
Being a springer, it isn't possible to clamp it in the workmate and force it to stay still, so the quality of my zeroing is somewhat dependant on the quality and consistency of my hold.

What I mean by zero is 'acceptable' accuracy.
Only now when I'm sending alot more pellets towards the target am I seeing trends that show me something is wrong, it would appear that before this had been hidden by my wobbles!

Pete

[Dave E]

I can't see that crossover could give you such a large error.
With the figures you have given I assume the horizontal zero is at 20 yds.
This indicates that the scope and barrel are out of line by about 2cm at the muzzle.
Assuming your scope centre is about 44mm above the barrel you could get that error by canting the gun by about 23 degrees of the vertical or the equivalent combination of cant and scope not set truely vertical with the barrel.

[whiteleggHW77K]

Right,

Did a bit more work on this, this evening.
Took the stock of and screwed the end of the receiver in a little bit more to make the dovetails line up porperly.

Seems a bit better.

With a few bits of packing to bring the front mount up a bit.
I have got it spot on at 25yrds.
But at 11yrds (my other zero according to chairgun) it is approx 5mm to 1cm to the right.

Now for hunting, provided this remains constant, I can live with.
Once I loose the cover of the bushes and wind and other factors come into play, a 5mm tollerance narrowing to zero is minor.

But it is still frustrating

I guess I need to shift the back of the scope to the right very slightly.
Will try slackening the right of the scope mount and tightening the left to see if it has an effect.

I will report back.

Pete

[whiteleggHW77K]

To Dave E

I will check the 'verticalness' of my set up.

I do have a bubble on the back of the stock, so I attemot to have a consistent cant or lack of it!

I can work out how to get the scope level, but how do I know that the rifle is level as well! where do I put a level to check that?

Pete