I have been looking a lot recently at tripod mounted rifle cradle and there are some great offerings although they tend to be in the $150 on up price range. I already have a nice Manfotto Tripod so I figured I would see what I could come up with and here is what I did for under $20 in supplies. I took a 3" ABS pipe coupler half of which you can see on the right in the last picture cut it in half and dremeled out a space for the nut in the bottom. Then I epoxied the nut in place and tapped 1/2 closed cell foam from a sleeping pad I had laying around to the inside. It works well and supports the 17lb beast of an AR-10 I have. I will be testing it at the range soon.