If someone tries to make it too big it's going to become a logistical nightmare.
You'd need a range for rent or a private property. The private property would be unwise to allow it without insurance.
The location would be better close to an airport than "centralized". Most folks won't drive more than a few hours, which isn't very far. Given our vast membership, a true centralized location is basically going to be smack-dab in the middle of the USA, which is to say Lebanon, Kansas.
Therein, you also get a lesson in the problem with averages, in that a location that averages the travel distances actually ends up being far away from pretty much everyone and isn't really convenient for anyone.
Moreover, while it won't be a problem in some states, it's entirely possible that state/local laws will make bringing some (or nearly all) firearms illegal. NY State, for instance, no outsider could bring any handgun, AR or any other "assault rifle" as defined by the SAFE Act.