This sexual manoeuvre requires one male receiving oral gratification from one (or more) female's. When the male in question ejaculates in the females throat, the female will the close her mouth and squirt out of her nose. Thus causing plenty of
spaff to
speed out of her nasal cavity, causing the Double Barrel
Cum Gun effect that is desired.
Dave: What did you
get up to last night then?
Matthew: After I finished I made my
missus Double Barrel Cum Gun.
Dave: Oh respect.