any snake close enough to be shot with a derringer is close enough to shoot your own foot off. if you have got time to shoot just step away. if the snake is on your property and may prove a danger to humans a sharp hoe or stout stick is more than a match for any snake. focus on a side arm for human attackers, wild dogs ect. a larger .45 colt or .44 with shot shells will do more than any derringer and is goo for other things as well.
on the snake shot/shot shell pistol issue. everyone that i have ever had had a crummy pattern. even a 10 inch TC Contender in 45/.410 got sold fairly fast. your milage may vary.
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Democracy is two wolves and a lamb voting on what is for lunch.
Liberty is a well armed lamb contesting the outcome of the vote.
Let he that hath no sword sell his garment and buy one. Luke 22-36
They all hold swords, being expert in war: every man hath his sword upon his thigh because of fear in the night. Song of Solomon 3-8
The man that can keep his head and aims carefully when the situation has gone bad and lead is flying usually wins the fight.