I have a S&W 4506 I purchased back in the latter part of 1990 and here to date, had never replaced any of the springs and was getting a bit concerned about that. So, I ordered a standard 14# recoil spring from Wolff along with a 16# jobbie just for posterity. There was quite a difference in the length of the new vs the old one and you can see the distance between the coils of the new one is more than in the old indicating compression of the old for a long time. The new one is about an inch longer than the old one and you can tell a vast difference when you rack back the slide. I'm sure the old one would have still functioned as I haven't shot it in several years but, I didn't want to change that anymore. I'm wondering about the rest of the springs including the five mag springs I have since all of them are 20 years old. Wolff did include another spring along with the recoil spring but I have no idea what it's suppose to be for and they didn't say in the packaging. It's short-about an inch and a half long and looks too large in diameter to be the trigger spring so not sure what it's for. At any rate, I think I'm going to get the mag springs and replace all them as well since they've been under compression for some time. I usually rotate magazines about every three months and have them numbered so I know which was used last time. I keep eight rounds in the magazine and simply after three months, go to the next one so the last one will have some time to "reset" itself. This way, with five magazines, each one only gets fully compressed every fifteen months.