OK--let me get the disclaimer business out of the way right from the start: this technique maybe (probably) exists already some place, especially since I'm a complete novice to precision scope use, but I haven't seen mention of it anywhere and arrived at it through my own (often wayward) imagination. So bare with me if I'm merely repeating something that is already known--if not, try it out and let me know what you think.
Obviously, this is useful mostly with higher-power scopes that use precision retIcles similar to the tremor, Horus, Mil XT etc that have extensive hold over and side hold "hash" marks.
I just scored a Leupold 5HD 7 x 35 ffp scope with the nice 60 MOA impact reticle and I put it atop my savage 110 LRH in 338 Lapua Magnum. I've found a pretty good load but so far haven't been able to get out to longer range shooting. Before I do that though, I wanted to test the tracking ability of the scope. I first used Litz's tall target test, and then went online and found something called the box test, which I like because it also tests windage along with elevation tracking.
Mt results, though, were pretty poor using both techniques. In both cases, my groups tended to open up a bit the further I dialed up from zero. Furthermore, it was a bit tedious getting multiple verifications of distance to the target, and then making sure it was level. Lastly, going home and doing the math, I noticed my error margins were often in the neighborhood of 10% or more.
Was something wrong with the scope? If so, what? Or was it just me (which is what I usually default to)?
I was pretty frustrated, not to mention feeding an expensive reload diet to get inconclusive results. So I started my feeble brain thinking about what was inducing error, and the first thing I thought of was I was generally changing the position of the rifle or the trajectory of the bullet, even if ever so slightly. So I thought up a way (again, forgive me if this already exists, just haven't seen it mentioned in my research) to minimize barrel alignment change relative to POI. At the same time, I figured out how to test the scope's elevation and windage tracking as well as the reticle's accuracy in the same shot--and to top it off the results don't depend on perfect distance calculation to target.
Here's how it works:
1) pick your ladder group distances. For example zero, then 6 MOA up, 8 MOA up and 12 MOA up etc. These are the distances I used on my sample target pictured above.
2) Use the standard formula of range yds x dialed MOA x constant .01047 (you can change the formula for milrad). Using this formula, I came up with 6.282" or 6 9/32" for 6 MOA, 12.564" or 12 9/16" for 12 MOA etc.
3) Draw a vertical line down the target surface and draw a horizontal line that meets it at a right angle near the top of the target leaving room for "overshoot." This is the zero.
4) From the zero center, measure down the distances calculated for your MOA changes and add a horizontal intersecting line. In the sample target, the first lower line is at 6 9/32" etc.
Shooting the groups
1) Shoot the first group at the top intersection--I like to put a target dot there (and at all the other line intersections) to make it easier to see. If it's off a bit--that doesn't matter and there's no need to adjust the scope. Use the same zero setting and magnification value for all shots.
2) Shoot the next group at the chosen MOA rise. For example, on the target above I dialed up 6 MOA and aimed at the target dot on the 6 MOA line below the zero line. At the same time, I dialed windage 6 MOA right. Lastly, I aimed at the 6 MOA target dot with a 6 MOA hold-over and a 6 MOA right "side hold." To help illustrate, here is a picture of the reticle, where the two red lines meet is the aim point used at the 6 MOA target dot.
3) repeat for other MOA changes within the capabilities of your scope.
My theory is based on "low dispersion" of group impacts as opposed to group distance from zero as a measure of the scope's tracking accuracy. Yes, I could be totally off my rocker, won't be the first time.
Here's the target group at zero line with the first 3 shot zero group shot and then the second 3 shot 6 MOA elevation and windage offset. Even if the absolute zero and distance to target are a bit off, the error does not appear to affect the precision of the group. The group was shot using a bipod on my caldwell portable table--I shoot in a quarry which is almost impossible to get a table level, so I decided a bipod would make leveling the rifle a bit easier. The "flier" is the very first zero shot, but the rest of the group is pretty tight. Although I only tested a zero and 6 MOA group--I'm pretty satisfied that the mechanical as well as reticle tracking are working well. Obviously a couple more MOA groups would reinforce that.
