So during the civil war in America, families use to send their daughters to help with the war effort and the women would be nurses. They would come and nurse the men back to help and just help with first aid needs. When the daughter finally returns home and theyre pregnant and they had to explain to their parents why they were pregnant, they gave them the following story: so basically, they claimed that they were in the line of fire of one of the enemy soldiers bullets. And basically as the theory goes, the bullet was shot by the enemy and it penetrated a soldiers testicle, passed through his body and hit the girl in the womb or whatever the fallopian tube or the girls ovaries. Some sperm deposited on the bullet and then went on and fertilized one of her eggs and thats how she became pregnant, hence the saying son of a gun.
Ruchie heard this story from an old American history teacher, Garreth Cole, when he was thirteen or fourteen. The story has American origins and as an American history teacher, Mr. Cole most likely learned this growing up in his Massachusetts home. Ruchie thinks that at least one girl has told this story during the war period and then the excuse was perpetuated throughout families. Since women were expected to be virgins until they were married, they had to come up with excuses that would keep their reputation in tact. It may have also started out as a joke, but the phrase son of a gun was catchy and so it was repeated. He likes knowing about these stories because it provides an alternative interpretation of events and it is interesting to see how people come up with these explanations.
I disagree with Ruchie and the validity of the story. Before hearing Ruchies story, I personally thought that the word gun replaced bitch in the phrase son of a bitch. Some people do not like to swear, so they say gun instead. A male most likely came up with this term because it is derogatory towards women. In order to compensate for their lack of ability to swear, they use a manly word such as gun as a substitute. Another explanation for this term could be that gun stands for a man in the army. Children that were born from women serving in the military could be deemed with the name of son of a gun. Nowadays, that meaning does not fit the term anymore, so it is less thought of. Most people just use the phrase in lieu of son of a bitch.