I would start with the barrel clamp at the null point
beltfed/arnie

Joe,
Just curious-- Why 7.2 inches from the mzl.?
We don't even know what barrel, caliber, etc yet
beltfed/arnie

Does that make a difference?

My answer is for traditional Schuetzen rifles with thirty to thirty two inch barrels. 7.2 inches from the muzzle is a starting point.   

           Joe. 

There is no exact science to clamp placement that I'm aware of and I've been shooting with a barrel clamp (rest) for some years now. Start at the null point or Joe's 7.2" back from the muzzle. It doesn't really matter. Shoot a group that you are confident is a good one, move the clamp a couple inches forward, fire another group. Then, move your clamp a couple inches to the rear of your starting point and again shoot a group that you are confident is a good one. Compare the targets for group size. If you see a significant difference in group size, for instance, if the forward group is tighter than the others, shoot a group with that positioning of the clamp and then move the clamp forward another inch and fire a group. I'll bet you see where this is headed. Keep tweaking the clamp location until you get the consistently smallest groups. You can do this in a single outing or you can continue testing for the rest of your life, your call.
I've never seen any real magic in barrel clamp placement but you will find a sweet spot by testing various clamp positions on your barrel. The main benifits of a clamp-on barrel rest is to help mitigate recoil torque and act as an aid in precise positioning of the rifle on the front rest, shot-to-shot.
I put a small mark at the sweet spot on the barrel with a black Sharpie. It is not apparent to the casual observer so I won't affect the rifle's appearance and is easy to wipe off if you need to.
Good shooting!

I believe you will find your technique is infinitely more important the clamp position.  When you look at the oldtime clamps, they have a v notch in the front.  That notch is to push against a firm pin with a heavy shoulder.   Most of your "benchrest sandbags techniques" will be altered.

I'm sorta inclined to the Schuetzenmiester school of thinking. I've rested a fair number of single shots on bags (never owned a barrel rest-yet), and mostly positioned the front rest where the rifle felt just a little bit butt heavy. Not the same for every rifle, of course. It makes my handling of the piece easy, and that makes me concentrate on shots more easily. As he puts it, "technique". Still, one of these contraptions seems like it has possibilities to help in that area. Thanks y'all. Pat

If you use the screw adjustment on the side of the front rest for Windage adjustment....With a long barrel and the clamp too far forward , it will make it difficut to reach the adjustment...I put my barrel clamp at 9 inches.

Terry