I once had an early war patrol in the Aleutians where I fired upwards of twenty Mk14's in rough seas, set to magnetic - with no prematures whatsoever. I thought it might have been the game modelling the difference in the Earth's magnetic field in Northern latitudes. Your run blows that away though....
Standard question - What mods [if any] are you running? If I understand Ducimus correctly, the Mag. pistol can be modded to give more or less prematures, but the dud rate is low and can't be altered. Prematures tend to occur in heavy seas. The impact pistol can be modded to give more or less duds, and, premature detonation isn't an issue.
So the question, assuming I've got that right, would be: What conditions are you firing in? Calm seas, close range and mag. pistol enabled, in the stock game, ought to give you the least amount of duds. The fact that you've had one suggests ...... Actually I have no idea what it suggests except that you obviously haven't unchecked the dud torpedoes option by mistake.
I don't want to be alarmist, but it sounds as if you have quite a karma debt building up there......
