Can't find my spin drift or coriolis.

[Topshot]

I can see how the rig provides a solid platform to align the scope in the verticle plane but as the scope body may be miss alinged Left to Right as well as having a 20 MOA rail, I find it hard to see how he is doing anything different than having a soild rest to work from?

[lisagrantb]

I don't know how to attach a picture but the way it's made not only holds the scoped action steady but it holds the scope and action centerline in almost perfect alingment no more than 36 arcseconds. This puts the scope almost exactly on top of the action and then you rotate the scope for alingment. It does this with the use of a machinest level that is secured to both the action and scope.

[Topshot]

lisagrantb

I worked for a long time in Survey and have experience in setting up plate bubbles. The accuracy of a plate level is determined by the radius of its curved surface and the size of its bubble.

The bubble on an anti-cant level is not a particularly accurate device. It is short and dumpy with a small radius curved surface. It is certainly not as accurate as the fine machinist level that you used to set up your scope.

As a test, set up and level your rifle on uneven ground, using your anti-cant level and then check it against your machinist level. Do this three or four times and I am sure you will get different results each time you try it.

As another test. Move the anti-cant level bubble 1 or 2mm from its central position and then check out how much it puts your rifle off level using your machinist level. This will give you an idea of the sort of accuracy that you can expect from your anti-cant level when being used while shooting out in the field under real life conditions.
You should be able to measure the angular error from the deflection of the machinist level.
I would be interested to see your results.

[lisagrantb]

You are correct, the anti cant device isn’t the most accurate device. If I were shooting without moving the crosshair the margin of error in the ACD would not make a big difference, but, when you adjust the crosshair as much as 30 moa you have just magnified your error considerably, that’s why your rifle, scope and crosshair should be as accurate as possible. Try this, put your rifle on a solid rest looking at a target. Cant the rifle a very small amount then dial in 30 moa elevation and watch what happens to the center of the crosshair, it will move in the opposite direction you canted the rifle not straight down. It may only move a fraction of an inch or so at 100 yards but at 1000 it adds up.

[phorwath]

lisagrantb,

Did you ever identify some spin drift or coriolis affect out on the field range? Curious if you worked on it any further.

Here's the tool I recently purchased and use to help ensure my scopes are mounted directly above the bore. It's already paid for itself (corrected a significant scope misalignment problem) on one of my LRH rifles.

EXD ENGINEERING : EXD ENGINEERING VERTICAL RETICLE INSTRUMENT - World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools

There's a picture of the device and some narrative explanation in this Thread:
Good Scope Mounting Tools

[lisagrantb]

Yes, I looked at the level you are referring to. I think it would be a good tool but I decided to machine one for myself (cheaper for me). I think mine is more accurate because of the tolerances I held and the level is good to .001” in 6”, I don’t know what the extra bit of accuracy gets me if anything at all over the one you have. And yes, the spin drift and coriolis is correct now, they exactly match the ballistic program. I guess you could use this devise and do some number crunching and deliberately cant your scope to match your spin drift and coriolis for a particular bullet and only have to correct for wind.

[rem]

if there is any wind at all at any point down range it will change your results.
try shooting further and maybe it will show up.