Hi, in your experience, could a scope failure cause a 7-8 inches round group at 200 m. or should it cause worse results? We checked everything else: stock screws, scope mounts, barrel and rounds are OK..... Thanks.

There is quite a few things that can cause that, but if you have already ruled everything else out, then yes, a bad scope can cause the problem you describe.

Did this just all of the sudden happen? With a good magnetic boresighter, you can do a quick check of the cross hairs by rapping on the scope with the handle of a mallet or something else that is non-marring while watching the cross hairs against the grid, or, if you have access to another scope, swap them out and try again.

Under good lighting, look the crown over real good to make sure there isn't any damage visible to the lands and groves. While you're there, look just in the bore from the muzzle to see if there might be a dark ring. Sometimes a buldge will appear right at the end and under bad lighting, can be a bit difficult to detect.

Maybe the wind, or the nut behind the trigger.
Pete

What caliber gun and what kind of scope are you using? Reason I ask is because some of the cheaper line scopes just can't handle the recoil of heavy recoiling calibers and jump all over the place. Also, how well does it shoot at 100 yards, it may also just not like the loads u use.

The rifle (not mine) is a Zoli/Husqvarna bolt action cal. 270 W, the scope is a (quite) new Bushnell 3200 3-9x40, almost no wind at the range. The owner said that in the past got better groups with that rifle; I tried it and got roughly the same results. We will make some tests with another scope.

I've had a scope do that when the rear lens in the erector assembly came loose. You could hear it rattle when you shook the scope. Started out just shooting poorly, then quickly went to 10" groups.

It's a very easy thing to check, so that is usually one of the first things I check by swapping to a known good scope. HTH, Dutch.

Expensive scopes can do the same thing. I had a Schmidt and Bender that started shooting groups in the 3" range. Put the Leupold back on and groups went back to sub MOA. This was on a 270 Win.