I think it's possible to do that much damage with a 7mm mag. Hard to say what combination of powder/lead one would have to use though. As far as the tags, I do exactly the same thing as you see on this deer. I attach my field tag near the base of one antler with a wire tie and then after I check it in at a game checking station I wrap the check in tag on the antler and use the small thin wire they give you to secure it. It looks exactly the same as you see in the pic.