The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

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Are telescopic sights truly parallel to the barrel? If everything remained the same, when a scope is
zeroed at 100 mtr and the bullet hits the bull, would the rifle still be truly zeroed at 200 mtrs, 300 mtrs
and so on away from the target?

I'm not talking about up and down, just left and right, I know distance changes elevation.

I have just recently bought an old used .308 and I was not too happy with how the scope was fitted. the rings were
interfering with the loading of the bullet and they also seem too small for the rifle so there is a lot of undue stress
on the bolts that tighten brackets of the rings to the rifle.

The way the thing is mounted I think the scope is left of centre of the barrel. Only a fraction, maybe 2mm or so.
If it was off centre, then it has been for a long time and it was always fine (so I'm told).

The question then, if the scope is left of centre and zeroed to 100 mtr, will the left and right change or will it remain
the same (assuming everything is constant)?

I got some aluminium off cuts and made some spacers to stop the excessive stress on the bolts and I have refitted the scope
and rings how I want them. I bore sighted it at a chimney pot about 120 mtrs away and the scope was off, not unsurprisingly.
The thing I am struggling with is when I bore sighted the scope to the pot I adjusted the scope in the opposite direct to what
I thought it should be????

With the barrel on the pot the scope was to the left, so I wound the scope right and it went further left????

The rifle did not move it was secure so when I the wound the scope left it moved right???

I assume that because the rifle was fixed and I was watching the scope move as I turned the adjuster, it moved in the
opposite direction than what I expected because it was the scope moving and not the riffle?

Normally if the rifle shoots left, you click the scope right and when you sight up again the scope has moved so when the rifle
is aimed it has moved right? Is that correct?

I have yet to fire it so I won't know until later what it is doing.

Regards

ozone

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Hi. When you're turning the knobs you're normally adjusting the point of impact that you want. Like you say if your rifle shoots left, you turn the scope right, which in reality moves the crosshairs left to meet the bullet impact. It's a bit counter intuitive!

I always think about it as the turrets moving the bullets in the direction you want them to go.

With regard to your alignment at distance, your windage (left and right) shouldn't change but as you get further out they will need refining, what looks dead center at 20m can actually be an inch out at 100 etc.

How parallel to the barrel your scope is depends on if you've got the right quality mounts and have them fitted correctly, but it's not essential to have them completely parallel, some long range shooters have mounts that cant the scope down to allow for long range shooting etc.

In general, more parallel you are the less adjustments you need as you increase your range.

Hope that helps, I know the lefty righty thing confused the pants off me when I first encountered it and I can still be found scratching my head at the sights on my pistol when I want to shift them!

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Thank you.

Yes very informative. Deep down I suppose I knew the sight moved in the opposite
direction, it just looked weird with the rifle fixed and adjustments made went the
opposite way. normally you don't see the movement because you put the rifle down.

So hopefully the fact that the scope seems left of centre should not affect it.

Thanks again.

ozone

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A 'scope is usually inclined with reference to the centre line of the barrel by way of a taper built into the rail, typically 20-30 MOA gets you out to longer distances as the usable range of elevation of the 'scope may not give sufficient elevation. As an example a 'scope with 50 minutes of elevation if mounted parallel to the bore will give you 25 minutes up and down from the centre line, add a 25 minute rail and you effectively get the full range of the 'scope for elevation.

For windage the 'scope is usually aligned with the bore for zero.

ovenpaa wrote:A 'scope is usually inclined with reference to the centre line of the barrel by way of a taper built into the rail, typically 20-30 MOA gets you out to longer distances as the usable range of elevation of the 'scope may not give sufficient elevation. As an example a 'scope with 50 minutes of elevation if mounted parallel to the bore will give you 25 minutes up and down from the centre line, add a 25 minute rail and you effectively get the full range of the 'scope for elevation.

For windage the 'scope is usually aligned with the bore for zero.

Yes I have that problem at Bisley on the 1000 mtr range I just do not
have enough elevation and I will get a 30 MOA rail to compensate,
but that is for my 223 and I expected it.

I was just wondering about the left / right zero on my 308 and the scope
not being central. If the scope was 2 mm left of centre and I always hit
2 mm right of aim I understand that but if I zero at 100 mtr and hit bull every
time, when I move out to 300 mtr, 600 mtr or 1000 mtr then the bullets will
progressively strike further to the right and I will have to allow for that.

Or do I always leave it at 2 mm off centre and allow when I'm aiming.

This is all based on perfect theoretical conditions with no wind or elevation.

Regards

ozone

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Even on an absolutely still day with zero wind the point of impact would start to differ from the point of aim as you move further away from the target due to the effects of the rotation of the earth and the rotation of the bullet (Coriolis effect and spin drift)

for best results the scope needs to be central with the bore and any inclination should be in the vertical plane.

you are expecting a lot of your 223 if your trying to shoot 1000m with it ! one of the top gun writers (vince bottomly maybe) did the 1000 with a 223 but used extremely specialist kit , fast twist barrels and 80-90g bullets. google it and It may turn up?

tackb wrote:for best results the scope needs to be central with the bore and any inclination should be in the vertical plane.

you are expecting a lot of your 223 if your trying to shoot 1000m with it ! one of the top gun writers (vince bottomly maybe) did the 1000 with a 223 but used extremely specialist kit , fast twist barrels and 80-90g bullets. google it and It may turn up?

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No sorry not a .223 a .308.

I was explaining in an earlier post that I understood the elevation issues
and used the .223 as an example. The issue I have (or had) was on a
used .308 I picked up over Christmas and made some changes to.

Thanks for the advice.

ozone

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