A good measurement of the depth of the rim recess will be a little hard to obtain, without pulling the barrel. You might just cut the head off a Hornet case and use it as a gauge .

Gary- 1in9" is pretty quick for a 5.6x35R, I suspect they used a 5.6x52R barrel blank to build it. I think the ones with smaller diameter barrels were made with 22RF barrels, like the earliest Hornets. Of course, I have no proof of this, it just makes sense.
Mike