Originally Posted by Brian Sampson
What you quite often hear is people quoting that if it's not centred you're not using the best quality part of the lenses (i.e. the centre) and if you're a photographer and you like to read up on lens specs and optical quality of the centre of a lens as opposed to the corners that idea will make a lot of sense to you.
However the lenses in scopes don't work in quite the same way as they do in camera's, so personally I think that theory is doubtful. I'm sure others will disagree with me and I'm open to be convinced to the contrary.
Yes it's the idea of using the best bit of the optics that I was initially attracted to, but I accept the point you make.
Having played with it and seeing what seems to me to be a shocking offset due solely to the mounts I am using, I think the merit could be more to do with having an optically centred scope allowing me to fix the horizontal offset in the mounts. The advantage of this would be that I have a good 13m indoor range and I thought that after some experimentation I'd be able to have a distance that I can zero to and play indoors with and know that when I go outside to play the rifles will be close to zero at 30yds or whatever we choose.
But - if the scope is mounted cock eyed to the barrel horizontally by 2.5cm at 13m (please follow and check my logic someone on declaring the error to be 2.5cm at the range 13m) and we zero to that at 13m, then at 30m the poi will be 3.3cm off horizontally... Is that right??? It sounds extreme - did I buy duff mounts or is it just my geometry that is out ?
Originally Posted by Tench
Try fitting both mounts together on the back half of the action, one with the clamp screws on the left the other on the right. Any misalignment shown will be double the actual amount the mounts are off centre when fitted. Centre split mounts like BKL can improve the centring of the scope. On some mounts the clamp shoe can be fitted either way up to accomodate different width rails. try to position this so the bolt face is as close to square as possible other wise the clamp can tip the mounts sideways when tightened.
Many thanks for that idea of mounting them together - an obvious idea that had escaped me! I looked at the clamp side to see if it was upside down or something, I will play with the idea that the mounts are tipping because of the position of the bolt and loose clamping side.
I had read this a while ago when I was researching getting back into the hobby, it went so far above my head I forgot about it. But having played a little and learnt a little I find it to be spot on to my level of understanding now - thank you.
One of my questions was going to be can I shim the mount clamp and this article answers this. I also have a milling machine and would consider taking a slice off the static side of the mount clamp.
So after some thought I think that my approach will be to zero this rifle at 13m and take it to a 50m indoor range tonight. My maths says I'll get as much as 7.1cm horizontal shift from 13m to 50m. That sounds like such a lot so I don't know if my geometry/maths is wrong. What I do know is it'll be obvious once I shoot a few pellets from a rest?
If the shift is that big I will optically centre the scope, I'll try the mirror and the V method, and then try and fix the mounts as best I can or put them in the bin as neither use nor ornament.
Thank you for the friendly sharing of knowledge and help guys.