I've just revised the design. Instead of embedding a bolt in the lead bar, I cast a plain lead bar & then drilled a hole in it, big enough to pass the bolt through it to screw into the camera's tripod bushing. It's made attaching the bar to the camera much easier. I've also covered the bar with adhesive backed felt, so there's no problem with either scratching the camera or getting lead on my fingers.
Here's another picture, this one also hand held but at the maximum 10x zoom. The Stop sign is several houses away from where I was standing.