I thought of this some time back and never really shared it with anyone online...
I wanted a way to stop my elevation turret from turning one rev too low, below my 100 yard zero. I think I've lost count of the times I've gotten mixed up as to which rev I'm on, wondering if I'm really back to my 100 yard zero or not.
You can count the hash marks, that's true... but I've found that with several scopes, it's pretty much impossible for me to remember which hash mark my 100 yard zero is on.
And counting the revs from bottom out? That works better in theory than in practice, again, for the same reason counting the hash marks doesn't work so well... I can't remember all that info for various scope I have... I get it all mixed up.
So... I have found that with my Nightforce NXS, I just made a polymer washer of the correct size to drop around the elevation turret and I sanded it to the exact thickness to stop the turret right at my 100 yard zero. Works great on the NXS...
For the Mk4, however, the turret cap goes down inside the outer housing, and I had to come up with something else.
I had the idea to put a rubber "O" ring inside that turret... I think this one is a #14 (?)... not sure. You can pick up an assortment at Lowes or Home Depot, and use what works.
Anyway, this O ring fits nice and snug around the inner part of the turret, and sits in the bottom of the channel that the turret cap runs up and down in... and it puts the brakes on going one rev too low--if you choose the right size O ring
... that part is important. Granted, it's more of a slow binding feel than a dead stop... but it serves its purpose, to keep you from going a full rev below 100 yard zero.
You can pick it out with a dental pick or just a safety pin with a tiny hook bent on the end of it.
This can't possibly void any sort of warranty on the scope, but I wouldn't leave it in there if I ever sent it back to Leupold... they might get confused, or worse yet fabricate some horse pellets to the effect that you damaged the turret, which of course it wouldn't.
The "O" ring is not a precise zero stop... all it does is keep you from going one rev too low... I actually got lucky with my last mount and found an O ring that literally stopped the turret at the zero mark... but if it goes a few MOA under that, you at least know where you are on the turret.
This may or may not work with other scope designs... you'll just have to experiment. Hard polymer or aluminum washers can be used in some instances, but you of course have to go to the trouble of making them or having them made...