After how many rounds do you replace your recoil spring? What are some symptoms of having to replace?

And a real FNG question but, but how do you know if you want a 16 or 18 1/2 lbs. spring? IS it preference, or different models take differently wieghted springs.

THanks
PJ

They recommend replacing it after approximately 2000 rounds. You can tell that your spring might be getting week if it starts ejecting your brass 10 feet away or more. I have heard that the spent shells should be about 6 feet away.
If your spring is too weak, it can cause failure to feeds, cause excessive battering on your frame, and other problems (maybe someone can offer more info here).

As far as the 16 or 18 lb springs, I just replaced mine with a Wolff 18.5, and it did extremely well in my pistol. Most factory springs are 16 lb though. Either one should be good, but if you think you might be shooting light loads, you're probably better off with the 16.