Rear sight shifted too far to one side

[nando]

Hi everyone,
I have a problem with the rear sight on my air rifle. I know it's not the fault of the rear sight itself because I recently changed it and I have the same problem as with the old one. Both the rear sight and the front sight are in the same position with respect to the center of the barrel, but I need to adjust the rear sight a lot to one side (to the right) or the shots go to the left. What could be the cause of this? I suspect there could be something bad in my posture or in the position of my head. Any ideas? How could I diagnose and fix it?

Thanks in advance for your help,
Nando

[Tim S]

Nando,

Is the foresight vertical? If the mount (or tube) is rotated over, that would explain why you have to click the rearsight over to centre your shots.

[nando]

Thanks Tim.

What do you mean by "vertical"?

It is a Feinwerkbau 800x and the tube can be extended but I have it as far back as possible. I have noticed that when moving it forward or backward it has a slight rotation clearance and if I extend it forward the problem gets worse, so maybe that is the cause or part of it. It is a strange problem, isn't it? Any idea how could I fix it?

[Andrew duryea]

I own a Walther LG400 and they have little notches in the barrel for the set screws, not sure if FBW has them but it would be worth the look. mark the current location of the tube with painters tape before moving it, just incase there aren't any notches.

[Andrew duryea]

also by moving it further out it increases the need for further sight correction. in theory to prevent this you would need to rotate the tube a couple mm (in your case to the left) when you extend it further out

[Tim S]

Thanks Tim.

What do you mean by "vertical"?

It is a Feinwerkbau 800x and the tube can be extended but I have it as far back as possible. I have noticed that when moving it forward or backward it has a slight rotation clearance and if I extend it forward the problem gets worse, so maybe that is the cause or part of it. It is a strange problem, isn't it? Any idea how could I fix it?

I mean is the foresight (the whole tunnel + mount) truly vertical?

The extension tube is held onto the barrel with screws. Can you loosen these to compensate for the rotation?

How well does the tube fit?

[nando]

Thanks Tim.

What do you mean by "vertical"?

It is a Feinwerkbau 800x and the tube can be extended but I have it as far back as possible. I have noticed that when moving it forward or backward it has a slight rotation clearance and if I extend it forward the problem gets worse, so maybe that is the cause or part of it. It is a strange problem, isn't it? Any idea how could I fix it?

I mean is the foresight (the whole tunnel + mount) truly vertical?

The extension tube is held onto the barrel with screws. Can you loosen these to compensate for the rotation?

How well does the tube fit?

The tube has a slight rotation tolerance. I will see if I can experiment with that, thank you for your help!

[nando]

also by moving it further out it increases the need for further sight correction. in theory to prevent this you would need to rotate the tube a couple mm (in your case to the left) when you extend it further out

Today I made some test at the range.

There is kind of a rail for the screws. It allows a little tolerance, but not much. I tried to exploit that, but the difference is very little.

While testing, a colleage warned me that I was located to the left of the target, what was making the problem worse.

[High Left]

Being 'off center' with the target will only make the holes slightly oval. I'm also thinking there's some rotation with the front sight you need to correct. Or maybe you used it to jack up your car to change a tire and bent the barrel? ;-)

[spektr]

I have an 800X... The stock adjustments are incorrect for you. If you have the sights all the way down
and your head is leaning a bit to the right, you run out of right sight adjustment to align your head.
Move the sights up. there are 4 levels of height adjustment. After your head is standing up, you can move the cheekpiece around
to place your head into the correct place. There is also an offset adjustment in the stock that lets you "joggle" the back of the stock laterally from the front. Its too hard to describe so go to the german feinwerkbau site and download the 800x manual. it shows how to make all the stock adjustments. Use them to place the sight line perfectly in front of your eyeball. that gets you the correct sight picture and stops you from running out of right hand windage.

[nando]

I have an 800X... The stock adjustments are incorrect for you. If you have the sights all the way down
and your head is leaning a bit to the right, you run out of right sight adjustment to align your head.
Move the sights up. there are 4 levels of height adjustment. After your head is standing up, you can move the cheekpiece around
to place your head into the correct place. There is also an offset adjustment in the stock that lets you "joggle" the back of the stock laterally from the front. Its too hard to describe so go to the german feinwerkbau site and download the 800x manual. it shows how to make all the stock adjustments. Use them to place the sight line perfectly in front of your eyeball. that gets you the correct sight picture and stops you from running out of right hand windage.

Thank you for your suggestions, I will look into that.

[nando]

Being 'off center' with the target will only make the holes slightly oval. I'm also thinking there's some rotation with the front sight you need to correct. Or maybe you used it to jack up your car to change a tire and bent the barrel? ;-)

Not that I can remember...

[Bob Foth]

The 800x has a convenient array of holes through the built-in sight risers. You should be able to move the rear sight base to the right or the front base to the left one pair of holes to solve your problem.
Since you said "Both the rear sight and the front sight are in the same position with respect to the center of the barrel", set the rifle vertical then look along side the riser/sight system and confirm both are vertical and parallel to check for any damage or misalignment. That system is nice, but not very robust if it takes a hit. I suggest always dropping the risers all the way down [u]to travel[/u] or removing them altogether.

[GoodEnuf]

Thanks Tim.

What do you mean by "vertical"?

It is a Feinwerkbau 800x and the tube can be extended but I have it as far back as possible. I have noticed that when moving it forward or backward it has a slight rotation clearance and if I extend it forward the problem gets worse, so maybe that is the cause or part of it. It is a strange problem, isn't it? Any idea how could I fix it?

I have the walnut stock version, left, of the 800x, the 800w. As described by Bob F. below, I have offset the sights to accommodate my stocky build and retain a vertical head position; also, I cant a lot, more than 10 deg., and get a good, heads up position. My front sight has an adjustable horizontal bar which allows me to verify cant consistency. To the point, the FWB 800x allows you to rotate the cylindrical part of the rear system so the adjustment knobs retain control in the plumb vertical and horizontal aspects. If you don't take advantage of the rotation adjustment, the vertical and horizontal sight clicks will bleed into each other, and make fine tuning of POI very difficult. Conversely, if you cant significantly, and don't make the needed adjustment to the rear sight, a lot of vertical adjustments will provoke an undesirable horizontal effect, maybe beyond adjustment range.

To access the adjustable feature (and verify that this is or is not the root of your problem), look at the rear of the the rear sight. There are several index marks either side of center and without canting, presumably the adjustable mark should be centered. If you cant, loosen the two retaining screws at the bottom of the cylindrical part, get into position including the cant, and rotate the cylinder until the adjustment knobs are vertical and horizontal, independent of the barrel. See the manual to verify my memory of this adjustment.

I think the posters were thinking your sight possibly was rotated without your knowledge, allowing for a horizontal offset which would increase with increased vertical adjustment. This offset, maybe combined with other factors, would put you beyond a correctable range.

Thinking on it, it is also possible the rear sight system is screwed down not parallel to the barrel. There is enough play in the two countersunk screw holes to get the plate off a degree or so; that would be enough to put the horizontal adjustment range out of the ballpark. Easy to verify - look down from the top and verify the the edge of the plate is parallel to the edge of the mounting fixture, then tighten. This should be done with the sight itself off the rifle so you can see what is happening.

By the way, I think poster Mr. Foth comes with substantial credits, if this is the same B. Foth of Olympic free rifle medalist fame, among other kudos.

JE