75 yards sounds like a far distance, but when you put it into perspective it really isn't. Consider many non-athletic men can run a hundred yards in say 12 seconds so they can do 75 in nine seconds. A deer is much faster so it probably only took her 6 seconds or less to cover that distance.
When the adrenaline kicks in they are super boosted and don't really know they are dead. Good job.
What does "gauge" mean anyway? As used here gauge means the number of round lead balls the same diameter as the inside of the barrel (aka the bore) that it would take to weigh one pound. It takes 12 lead balls the same diameter as a 12 gauge barrel to weigh a pound. The smaller 20 gauge would require 20 balls of that barrel diameter. The larger bore 12 gauge would require 12 lead balls of the bore diameter to weigh one pound.
In general the number of pellets in a shotgun shell...