Cornered, with weapon wielding BGs.....hmm, sounds like a defencible self defence situation to me, I would pull it out, declare that I will shoot them, and if they approach any farther, I will start shooting, if they approach any farther, Id shoot one of them once, then see what they did, I would expect that they would scatter, but if they didnt, I would shoot till I ran out, or the threat was gone. If you aren't carrying enough rounds, then thats your fault. I have found that a glock 22 with +2 extension carrys 17 in mag, 1 in chamber. Multiple threats without weapons in same situation would also be justifiable for drawing and shooting, because there is treat of grevious bodily harm because of the number of them, they would easily overpower you, and could kill you with bare hands. Also, if you can conceal a gun, magazines are smaller than the gun is, and I dont see why you couldnt carry spares. This depends on where you live, but I wouldnt be cought dead in a dark ally at night, no matter what the reason, except to chase after a loved one who should have been told to stay with me at all times.
Course, Im 6'3" and 215lb, so I can get away with the big gun
"Where the choice is between only violence and cowardice, I would advise violence."
~ Mohatma Gandhi