The Russan attachments are pretty bomb proof and very repeatable. Mine has never shifted and it gets lots of work and a rough time.
The key to the whole thing with clip ons is to sight the clip on in with the particular scope (you are getting the thermal and the scope in perfect alignment). You can only do it accurately by firing shots and adjusting the X&Y coordinates. You only need to do it with the thermal once and then it doesn't matter what alteration you make to that particular scope zero.
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