You are not wrong about expanding- just not sure if enough to matter. But the heat may loosen Loctite if it happens to be present. Personally, I've never come across scope ring screws that ever needed anything other than a correct fit of the tool to loosen. Granted, some were tighter than others, but they broke free at a reasonable amount of torque. I can't emphasize enough to have a proper and well fitting tool. Also apply some down force on it as you twist. If your rings are like mine, I'd use a T-10, but some brands of T-10's fit better than others. Use a quality made bit if it is a Torx. In case the tool is second rate, it could be soft or under-sized and slip.