One of the first "gun books" I read was Combat Handgunnery by Ayoob (forgot which edition, years ago). One of the things that stuck with me is that he said in the event that you're within arms length and the BG goes for his gun... you go for his gun too. At the very least control his muzzle, and it can give you much-needed seconds to draw your own weapon.Excaliber wrote:A well practiced disarm might work - but remember that in such attempts, the gun fires around 90% of the time, so you'd want to make sure your initial muzzle redirection move is really quick and effective.
I thought so long and hard about it (without practicing) that I did it without thinking once in a scenario-based training exercise with some local law enforcement friends. I had performed a traffic stop, returned to my vehicle to check paperwork, and when I returned the "driver" whipped out a pistol. Before it could even aim at my chest, my hand was already on it, holding the slide and pushing it away to the front of the car... I didn't even realize I was doing it until I was finished
It hadn't even occurred to me to draw my own weapon 
Keep in mind that I had never practiced it up to that point, and I'm FAR from fast. It worked well though, and I was surprised... and so were the others.
