Appears to be western Irish slang for 400ml of vodka. May have been used in old Russia where the term got picked up.
An average shot taken straight.
Ben: I had a nagan of vodka last night
Jerry: Bet that warmed you up
by nat2000 September 5, 2006
Get the Nagan mug.
A group of people who cause trouble. These kind of people are typically found in the ghetto and poor white neighborhoods.
Those damn nagans stole my car again.
by davelk August 4, 2006
Get the nagans mug.
A Daddy Nagan is a term used to describe a "shoulder" of spirits.

This slang is predominantly used in the north Kildare amongst alcoholic youths.
Person 1: Story boys, Anto, tell Johno to tell Deco that I want a Daddy Nagan of vodka for the session I'm going to
by YOURMOTHERTHINKSIMHOT August 24, 2009
Get the Daddy Nagan mug.