You are confused about what a case gauge does,
and does not do.....
♥ A case gauge checks the exterior of the cartridge for
external physical abnormalities, like burrs left by extractors or trimmers, out of spec case bulges, and over size expansion of a case due to Major PF. It will also check for concentricty of the cartridge, and check the roundness of the case.
♥ A case gauge does NOT check OAL or how the bullet sits relative to the rifling in the barrel. Only the barrel can do that.
Again, once you know that the gauge matches the barrel for size, the check is: Does the cartridge fall into and then back out of the gauge
using ONLY the weight of the cartridge.
PS. Reloading ammo for your pals is a VERY bad idea on several levels. Allow them to come over with their own components and use your equipment, but do not reload for them. I assure you, their widow will have no issue with taking every penny you ever expect to earn at the first available opportunity.