I have read that, early on (Viet Nam), that, at the request of the Teams, S&W developed the model 39-the original hush puppy, but they further requested a "high capacity" 9, and the model 59 was the result. I have read this in a couple of places, and other than that, I can't say. But I have owned a 59for over 25 years, and have shot a large ammount of all types of ammo through it, including foreign stuff, blazer, hand loads, and anything there was, and I can not remember a failure that was the fault of the gun. There were many 15 round magazines that were fired as fast as the trigger could be pulled. It would shoot them without a glitch. I bought it used, and never touched it internally. Now I own 2 of them, just in case! flapjack