Apparently they were let in, then arrested, then released without charge and their guns returned as they hadn't broken the law. However, they were there protesting against the 'Mulford Act' that intended to disarm them, and it was subsequently passed. So they didn't get shot, but they didn't get what they wanted either, and they did get banned from doing it again.
Of course, there's a lot more detail than I've put into this post, and society was pretty different at the time. Reagan supporting gun control? The NRA as a sporting organisation that supported gun control? And the panthers were Marxist? So I'm not sure it's a very instructive example about how the same thing would go today.
[1] https://en.wikipedia.org/wiki/Black_Panther_Party#Protest_at...