How many rounds in Glock 21 magazine?

[Firepower!]

Hi
I would like to know how many rounds do you load into your regular Glock21 magazine? I use to do -1, but now I load 'em up to full 13 rounds or 15 if +2 extension. Many folks think that -1 or less than full capacity is a good formula. I agree with them, generally. However, I have been asking around and doing to research on Glock magazines, and found out that the spring does not go bad even if you load them to their full capacity. What is you view on this?
Thanks.

 

[Haifisch]

Throw 13 in there and rock !!

 

[jersey_emt]

The standard factory magazine is designed for 13 rounds. Load 13 rounds.

 

[JohnKSa]

Years ago I recall some reports of Glock mag springs failing earlier than expected when the mags were loaded to capacity.

Haven't heard any in quite some time so I assume that whatever was causing the reports has been dealt with constructively.