This is the first time I have seen one of the Dubro mounts flex that much, I even run A small RCS 1.40 gasser with one of there mounts without problems, I think I have 6 or 7 of them??
I'm going to show you an old mount I have from the pattern days, I have A couple of these too. They don't say who made them on the casting but I "think" they are Dave Brown anti vibe rail mounts, these don't flex and there is no vibration. I know I got them through Central some time ago. The Hyde nose ring mounts work great but that would be the first Magnum 70 I have ever seen needing one. I also have the solid OS mount for my OS 1.20 and I use the Jtec anti vibe on my YS 1.40, I love that mount but it's not an easy one to install on your fire wall but it sure works!!
There really are A lot of good mounts out there to choose from. Have you mounted that Dubro some way different?? Just wondering, A .70 Mag pulling it over???[:-]