Forget about anything else, what is the toughest scope on the market today?
Ignore the prior answers.
Yours is a good question and, as you would expect, there are several variables or components to consider.
The first one is obviously the main tube. Here we can quickly cut through the chaff. The vast majority of scope tubes are made of aluminum. There are a few that are made of steel and I have no first-hand knowledge of those so this discussion is all about aluminum tubes. You can immediately eliminate the 1inch and 30mm tubes from the ranks of the toughest scopes; their tube wall will be a maximum of 2mm thick. Then you are faced with the 34, 35, 36, and 40 mm tubes. In the 34 mm tubes, if the range of adjustment is much greater than 60MOA (or about 20MIL), the tube wall will 2mm thick also. For example, I know that the 34mm tubes from March are all 4mm thick; extremely strong. I also believe that some Nightforce scopes are 34mm and have thick wall; the NXS series is not one of them. There are many other brands with 34mm tubes and thick wall. But again, I come back and say 1inch and 30mm tubes do not make the cut.
Next is the design of the tube. If it's a two (or more) parts main tube, they don't make the cut. If the objective bell is extruded, they don't make the cut.
If the tube is bent by accident, your zero will shift, to say the least.
After that, you have the knobs and the magnification ring. Now, any scope that lands on the elevation knob may get damage to that assembly. Some are tougher than others.
Let's talk internals. The first thing that comes to mind is the erector tube. If you have a heavy erector tube, any hit on the scope will cause more internal stress on the knobs and springs than if the erector tube is lighter. But if a light erector tube is not engineered properly, it will be easily damaged. You also have the choice and use of proper material for springs and knobs and so on. Some last longer than others.
Then there is the issue of how everything is assembled internally and sealed overall. Again, one piece tubes are superior to multi-piece tubes for sealing. I've also seen scopes with an access plate to the knob assembly. That's not conducive to sealing life.
Internet lore is one thing; real life engineering is another.
