Remember me saying we have a Schultz & Larsen for Jagtfeltskydning?
Well the S&L needs a few minutes of angle on the ‘scope rails to bring the Kahles to something close to useful mechanical zero, by this I mean when you wind the elevation drum down it bottoms out at around the chosen zero for the rifle. OK, why should I want this? Well a ‘known’ mechanical zero helps to prevent the shooter becoming confused in moments of stress, the last thing I need is to get lost on the number of turns the drum has been wound, and have to wind it back to the very bottom and then forward say a turn and a bit to get to my chosen zero. With me so far? If not humour me here as it is just the way I prefer to have all my rifles set up and it is so much easier to wind the drum down, feel resistance as it bottoms out and immediately know I am at 100m.
The ‘normal’ way to set a mechanical zero is to shim the rear mount which places undue stress on the tube, or leave it alone and just have a zero somewhere in the middle of the elevation travel. Neither are acceptable so I am off to machine some taper inserts.
I will take pictures along the way. Usually people only publish successes with such things but in the interest of science I thought I would publish the whole thing.
I know how much elevation I need on the rear mount, it is 1.31mm, this was determined by some math a while ago and got me to exactly where I wanted to go so it is important to replicate this rear elevation shim.
The plan is to machine a length of aluminium at the correct taper and for the same distance as the rings are set apart (130mm) then drill for the rings, cut a piece off each end and fit the shims under the rings, so in theory I have the correct taper and the ‘scope is held in a stress free method.
After this I can bed the ‘scope to the bottom section of the rings to complete the job.
Whilst I am at I will be swapping out the bottom mounts as the existing ones shift under recoil and I have a set of Apel mounts with a recoil lug built in.
You can see the difference here between the front mount with the recoil lug (right) which engages into a hole in the front mount.
First thing is find a suitable piece of aluminium for the rail and machine it to the correct length and width for the job, 130mm x 21.5mm then turn it on it’s side and machine a relief on either side, I will need to cut the shims out at some point so the relief is the start of this.
Now I know the elevation needed is 1.35mm so I place the work piece on parallels and then add a 1.30mm slip at one end, as the slip is just under the edge of the work piece this is not strictly correct but I can at least tighten things up and then use a clock to confirm the difference over the 130mm.
Crikey! It is 1.35mm! Life is not always so kind in the workshop so I run a 20mm cutter across the top of the rail until it has a cut across the full length. In theory this now gives me a taper with a difference of 1.35mm and checking with a micrometer confirms I am correct. For those of you that work in imperial the taper is within a few tenths of a thou across the distance.
The taper is drilled at this stage for the mounts and two passes made across the work piece to give me two pads.
I am starting to wonder if it is really worth all the hassle doing this but I am not shooting today and it is fun finding out.
Part two to follow…..