Yes, this is what I did, but when it shot so badly, I had a closer look at everything. (I had fired two groups of five shots at that stage, and things were improving but it looked to be "double grouping"). Second lot of five shots (numbered for sequence fired):

I checked that everything was tight (ring screws, base levers) and they were. I noticed that I could see light under the RHS of the front base. Sure enough when I undid the levers, I could rock the scope on the bases. So I went all loosened everything and attached the mounts to the rifle, making sure that both front and rear contacted the action properly (ie no rocking) and then did up the ring screws. When I undid the levers, it still rocked!!! So I did the procedure again and basically got lucky. I couldn't believe that the the rings were actually twisting the scope tube.

It still seems to take some settling. The next five shots seem to show it wandering toward a common point, but I ran out of ammo at that stage - last week I sighted in my 375H&H with only 6 rounds when I installed Warne QDs on that rifle, so I thought that taking 15rounds for the 458 was being conservative.

The last five shots after getting the proper base contact (numbered for sequence fired):

This is my third set of Warne QDs and the first two sets didn't give me any issues like this.

[PS: I meant to post this in the Big Bores forum - no wonder I couldn't find it this morning.]