Let it never be said that this forum isn't educational.
The challange acceptance named a place I hadn't heard of. A little rooting about on the internet and this turns up:
RiflesOnly
500 yard
moving target range
Looks like a "must do" when visiting relations in Corpus this summer. Although my first priority will be getting reasonable groups out of the (seldom used) Sendero that's been gathering dust in my safe. We'll save the moving targets for a later visit.
Thanks Rich!