The SSK Industries T'SOB mount has been around for a very long time, and was designed for securing scopes on heavy recoiling hand guns. It allows for up to four rings to be used. I have one on my .475 Linebaugh, which doesn't weigh any more if as much as your 4" 500, and has plenty of recoil. It holds my Leupold 2x scope in place with only two warne rings. This is exactly what they were designed for.
My Freedom Arms 83 has a 7 1/2" octagonal barrel on it. That's another thing nice about the T'SOB, it gives you a variety of positions to mount your scope. If you know what a piccatinny rail is, then you know pretty much what the T'SOB looks like.
