Can you explain what the mechanical problem within the scope are and how they manifest themselves. I've read your comments on Leupolds earlier and now Swaros here. I'd just like to understand what the problem is and how it relates to use on a hunting rifle - I don't doubt it, but I've never pursued a higher understanding of what goes on in a scope. What is actually happening with the tracking problems? For a rifle where someone wishes to dial out to 4-500 yards what is the magnitude of the issues? I have not noticed issues with mine, but I'm not testing in a formal way. I'd be happy to be directed to somewhere to read about this as well. Thanks!
I would google "scope internals" then click "images". I'm sure that you are familiar, however basically a scope is a tube in a tube with some glass, erector spindles, and srings. The inner tube houses the reticle. The parts that move when you adjust the turrets is the erector system. If you imagine looking at the scope from the shooters perspective and seeing the outer tube, and the inner tube with two micrometers (turrets) At the 12 and 3 o'clock, and a spring (erector spring) at the 7:30 o'clock pushing the inner tube against the the turret assemblies. When you make an adjustment the turrets "screw" the inner tube in or out with the erector spring holding it (the crosshairs) in place.
For zero retention the whole erector system MUST remain completely static at it's set point. Any movement by the erector spring (fatigue), any movement in the internal lenses (binding agent, thermal expansion, etc), or any movement of the outer tube (flexing), etc, and you will have a zero shift. It doesn't take but a tiny bit of movement to cause major issues. If we look at normal hunting scopes (all of them regardless of brand) they mostly use erector springs that take a set and fatigue, feature glass to metal contact that exaggerates thermal expansion movement, and thin outer tubes that bend and flex relatively easily causing impact shifts from bumps and knocks.
For correct adjustments (tracking) the erector spring must maintain constant pressure on the inner tube and have no burrs to create inconsistencies, the turret screws must be threaded perfectly with no inconsistencies, and their must be no influence on the entire erector system.
Now as now as for what causes issues in scopes: big picture it's really simple- manufactures design and build scopes for their average user. The average user know nothing about functioning, doesn't truly get a solid zero, shoots very few rounds (maybe not even a box a year), treats his rifle gentler than a new born baby, only thinks about "glass" so he can brag to his buddies, and believes all scopes "work".
Specific problems are thin tubes, weak erector springs, turret spindles/screws incorrectly machined, etc, etc.
To the heart of the matter- how big of deal does it all make to the hunter wanting to hit at 400-500 yards? Quite a bit actually. Before they hit 500 rounds the vast majority of Leupolds, Nikons, Swarovskis, Zeiss's, Meopta's, Minox's, etc will have significant issues. Around 6 out of 10 Leupolds show issues straight out of the box. Of those that initially worked, within 250 rounds or so most Leupolds that are used to dial, will have enough of a problem to cause a miss on a deer sized vital target at least once.
But how can that be? Most say they never seen a problem, right? Again, go back to the average user or even slightly above average user. He shoots three shot groups (statistically insignificant thereby never truly seeing the true center of his group or Mean Point of Impact), changes ammo often/fiddled with loads, when he shoots at distance he generally shoots at extremely large steel plates or rocks and only for a few rounds, usually if he hits anywhere on the plate he's satisfied, if he misses he generally blames it on himself or conditions. With all of that, he's still only shooting a very few rounds in total.
If he had a scope issue even 10% of the time, where in that scenario is he going to recognize it? Yes, it'll happen and cause a miss, but most of the time it won't be recognized as a mechanical problem. That's where testing and shooting comes in. It shows what the scope is actually doing and where any issues might creep up.
I can can tell you this- I used to teach shooting courses for hunters to extend their normal hunting rifles from 0-600 yards. In hundreds of scopes and rifles every single hunter loved their Leupold/Zeiss/Swarovski/etc scope when they showed up. The catch is I never had one leave the two day, 250 round Course happy with their Leupold/Zeiss/Swarovski/etc scope. The reverse is also true- I never had one disatisfied with their Nightforce/SWFA SS/Bushnell HDMR/LRHS scope.
Really it it comes down to whether the task will show a .5-2moa shift and/or a significant error in tracking. If you are trying to shoot deer at 350+ yards then the answer is yes.