If you're limited to their ammo, it doesn't allow you to test rounds you want to.
Yeah, I just got these steel core rounds, and I can't test them at your indoor range if you make me use your "safe" ammo...
I promise it wasn't me, Zimm!
Seriously though, is your Brother in Law's range indoor, or in a city? There might be another reason they want to know exactly what ammo you're running.
https://www.indianagunowners.com/fo...he_idiot_who_damaged_kodiak_firing_range.html