I fell for it too, the hornady gage is cool but not all that practical.
Buy the Sinclar or make your own with some bb's or V holders.
Better yet, you have half of what you need on the Hornady already, just add some v holders to it and reverse the concave head holder to the flat side for your end stop......I have a new mission
Scope rings almost work
....I'll find something laying around here to mount to it.