DRAFT, short story idea

 Posit..

In an undefined time and place, a man finds a weapon.  A soldiers weapon. Picked up on a battlefield gone quiet and passed by.  The fight has moved on.

The man, older, retired, living alone on a planet outside the center of civilization. 

The weapon, rifle, is a sniper tool.  It's also run by an SI, a synthetic intelligence.  It's a military weapon, and designed to work only with the soldier assigned to it.

The planet has been invaded, threatening the mans home.  His retirement home.  He finds the weapon while scavenging around battle sites.

The man is retired military.  Combat veteran, at least a sergeant.   He knows the weapon, and tries to bamboozle it into operating for him, even being not the assigned soldier.  It doesn't work, but in the process he describes how he knows about such weapons.  How he had one for years.  He named his F.R.E.D., against all rules.  They talk about Fred and their lives.  They build a relationship. 

In the end, the weapon does work for the retired soldier, explaining that he (the weapon) was assigned to the same unit, and also knew Fred.  They were friends.

This sounds familiar.  Is my brain dredging up a story already written?