Thanks guys. I've already got a Racker on my Shockwave and love it. It's just a matter of getting the correct grip before shooting. I've managed to do that with the Shockwave, and I think I can do it with the 500. I've already bought some goodies from Defender Tactical and a TactaLoad stock for it. I'm sure I'll pick up a 28/30" barrel so I can hunt with it as well.
John A: I like the first item you linked, but I won't be using an extended mag tube. If I can find something like that but for a standard tube, that's what I want.
Ernst: I'm interested in the solution you mentioned. Got any links to this? I'd just like to see how it looks and works before I make a decision.
Thanks to both of you for the ideas.