Rick,
On African safaris far more shots are fired, especially on a longer hunt, and in particular on what are called "cull" hunts. These started becoming popular maybe a dozen years ago.
In South Africa (and in other countries both in Africa and Europe), game belongs to the landowner, and can also be sold in markets and restaurants. Thus it's income to the landowner. In Africa they used to hire professional cullers to kill excess animals and process/transport the meat, but eventually found safari hunters (and especially Americans) would pay them to shoot cull animals, especially if they could also take trophies if they ran across one. In return, the hunter gets to hunt at a reduced price, but often still pays a small per-animal fee. Often dozens of animals are taken by one hunter. Have been on a few of these, among others once spending a month in RSA while three different groups of hunters came and went.
All the hunters range-check their scopes upon arrival to make sure they're on after being on several planes, before going hunting. Aside from many scope being mounted on rifles chambered for harder-kicking cartridges, I suspect bouncing around in Toyota Land Cruisers takes it toll. I say this because on one of the two scopes that I've had fail on my African hunts, the objective bell spontaneously started to unscrew itself after a few days.
Usually what happens, however, is a hunter who's been making one-shot kills suddenly starts making bad shots. Whereupon the rifle's checked over, first for the tightness of action and mount-screws (which most experienced safari hunters check frequently anyway) and then at the range. So yes, scope failure can easily be determined.
The other scope I had go bad was a $1000 3-9x on a .375 H&H. The rifle shot shot right where it had been sighted-in at home upon arrival, grouping very well, and over the next couple of days killed two animals, the bullets landing right where they were aimed. Then one shot was somewhat off, though it still killed the animal. I thought it might have been my fault, but later that same day I aimed at the chest of an impala ram, and instead killed the female standing next to him. At the range the rifle was still shooting inside an inch vertically, but spreading over a foot horizontally. I put my backup scope on and had no problems from that point on.
Have seen problems on a bunch of scopes over there, and on a few multi-species North American hunts as well, often after a few plane flights, or riding horses 100 miles or more. But usually they occur on a magnum from .300 up. Haven't seen as many scopes fail on North American big game hunts, both because of lighter-kicking rifles and far fewer shots fired, but one was a 4-12x on a .240 Weatherby.
As mentioned in my previous post, when I test new big game scopes I normally mount them on a rifle of at least .300 magnum recoil, and they fail most often do so within a couple of boxes of ammo. But sometimes they'll work OK on a milder-kicking rifle, then go to pieces on a harder-kicking rifle.
That $1000 3-9x that failed in Africa had worked fine on a lightweight .30-06 for over a year, including at least a couple hundred rounds shot while testing of various handloads, so I switched it to the .375 and sighted-in before flying to Africa. It failed after around 20 rounds on the harder-kicking rifle.
I also know a gunsmith who makes a lot of larger-caliber hunting rifles. He used to range-test the rifles with the scopes provided by the customers, but grew weary of so many of their scopes failing on rifles from .300 Winchester Magnum on up. Since his rifles cost several thousand dollars, the customers did not provide cheap scopes.
Maybe 10 years ago he finally refused to mount customer's scopes, because he was wasting too much time having to take them off and mount his own test-scope--a fixed-power tactical scope.
Aside from an objective bell unscrewing, the common symptoms are:
Scopes that refuse to stay zeroed. Often they can be rezeroed, but within a shot or two they'll be off again by up to a foot.
Broken reticles. Haven't seen this happen with an etched reticle, though one African PH said it happened to a client's scope.
Groups growing larger. This is usually due to a reticle cell or erector tube coming slightly loose inside the scope. Have seen rifles that were consistently sub-MOA start shooting 3-4" groups at 100 yards--and when the scope was switched, start shooting sub-MOA again.
