It doesn't matter what it's called, they'll continue to oppose addressing it
That doesn't mean we need to make it easy for them to oppose it. Don't give them a stupid way to dismiss the conversation before it even gets off the ground, make them actually defend their position that private sales shouldnt need background checks.
IMO, getting stuck calling it the gun show loophole when there are better things to call it because that's what everyone has always called it has the same kind of energy as conservative assholes who refuse to learn a person's pronouns or old people who never bothered to scrub things like "colored" or "oriental" from their vocabulary. Language can, does, and should change with the times, and we need to keep up with it.