Repeatability is the feature that is totally indispensable for a long range riflescope. Most scopes claim repeatable shooting. That being said, you shouldn't rely solely on their allegations. A meticulous analysis of your scope's results for repeatability is a must. A scope that does not meet the high requirements that you need for a long-range job will have to be rid of.
Scope repeatability issues have to deal with windage and elevation adjustments. That is why, you will have to test both adjustments to see whether or not the results they produce are repeatable.
Zero repeatability
This test will help you to ensure that the scope you are using is consistent when it comes to its 'zero' starting point.
First of all, make sure you are using an accurate rifle with a cool barrel. This is essential if you don't want to dump a fair scope and be left with a lousy rifle.
Mount the scope according to manual instructions. Take extra precautions to ensure that the rifle is stable. For that purpose, rests and a firm bench can be used. You won't need any wind here, as it may distort the results, so only conduct this tests on a calm, windless day.
Zero the elevation turret and make a shot. Then turn the elevation turret a few times through the entire range and get it back to zero. Shoot again. The two shots should fall in the exactly same hole, no deviations acceptable. Then randomly spin the elevation knob through several rotations and dial it back to zero. Make another shot and check if it's repeatable. A good scope should have no problems here.
Do the same test with the windage turret. Naturally, windage adjustment is very important at longer ranges, so you'll have to make sure it's as solid and reliable as the elevation adjustment.
At the final stage of the test, play with both the windage and elevation turrets. Change the adjustments randomly and then zero both knobs and shoot. All the bullets should again fall in the same hole. If this doesn't happen and what you see looks more like a sieve, the scope is useless. If the results are fine and you see only one neat hole, than pass on to a more serious repeatability test.
Linear repeatability
Now we have to make sure the readings on the elevations and windage turrets really mean what they say. The turret may seem reliable when doing the zero repeatability test but turn out complete rubbish if we try to observe some of the specific adjustment results that the knobs produce at MOA clicks.
To begin with, install a target at some 50 yards before the rifle. Zero the elevation turret and shoot. Then rotate the knob one full time and shoot again. Repeat the procedure a few times until you reach the upper adjustment limit. The trick of the test is to
a) see whether each rotation stands for equal MOA intervals and
b) confirm the stability of the horizontal windage adjustment.
What you should be able to see at the end of the test is a straight vertical dot line with equal distance intervals between the holes.
The same test is perfectly applicable to check the windage repeatability, only this time, what you will eventually get, will look like a straight horizontal line with several holes on both sides of the dead centre, neatly aligned at equidistant intervals.
Repeat the test several times to be sure that the selected scope is repeatable. Then scale down to using 1/2 revolutions instead of a full one. An ideal scope should run no problems with this.
Finally, complicate the test by checking both windage and elevation accuracy at the same time. The result will look like a nice diagonal line beginning from the dead centre.
At last, the repeatability of your scope is confirmed. Now that you are sure that the manuals are not lying, we can proceed to other, more particular and sophisticated adjustments.
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