Bro measure out 19 feet. Actually..before your John Wayne self even goes that far Mr Doc Holladay...
That sounds reasonable to me. The element of surprise would be key though.
I know absolutely zero about any martial art, but I'm well trained and well practiced with my carry of choice, a Glock 30 (subcompact 45acp) and I know quite well how long it takes to draw, accurately aim, and fire my weapon. Factor the impact on aim during stress situations and the surprise element of not expecting a bad guy to even try a move like, and I can see a fast, evasive opponent having a good chance of closing 20ft before I could put one in him.
I had to draw my weapon on three bad guys once, and even the baddest freeze when they are confronted with someone who's stance, manner, and eye contact suggest they are willing and able to shoot you if you move an inch. I think very few armed people would expect someone from that distance to bolt forward, weaving and dodging.