I've listened to recommendations from various gun makers, as well as a major spring maker.
The gun makers who do a lot of LE/Gov business often offer some recommendations on periodic mag spring replacement. I've seen those recommendations vary over the years, and it usually seems the result of both engineering input and their LE/Gov customer experiences and feedback. Sometimes the recommendations have also varied due to caliber (increased slide velocities and feeding 'timing' considerations of different calibers).
I started marking many of my magazines left loaded for long periods with mo/yr dates marking when new springs were last installed. I check them each range session, as well as during occasional armorer bench checks, and will also mark some (check mark & date) to indicate they've been tested/checked in live-fire and remain serviceable.
I also compare the free length of service mag springs to new springs. (That used to be a recommended bench check by at least one of the major gun makers.)
When I asked a major spring maker about mag spring service life expectations one time, the number of rounds-fired they told me was a lot less than what is often heard expressed by many shooters online.
Then again, think about the folks who say their motor veh oil can last a lot longer than manufacturer replacement interval recommendations.
I was told by one of the gun companies, and a spring manufacturer, that bulk spring shipments may number up to as high as 10K units at a time (for their company customers). We expect a lot from a simple wire spring, and it's not like each and every spring in that 10K batch is subjected to individual testing before being shipped, is it? (I was told no.) If there's a materials, manufacturing or heat treat issue with some spring - or batch of springs? Well, that's what we hope to catch before it becomes a problem that manifests outside the range, right?
As a firearms trainer and armorer I've seen my fair share of folks experience problems during training drills and quals that ended up being caused by weakened magazine springs. It happens. Sometimes it's been a surprise to folks, and other times it's been a shock, and other times it's something they acknowledge and say they knew they were reaching the end of the spring's service life. What, were they trying to wring our every last round of use before replacing it with a new one? The cost of new springs can often be inexpensive insurance. Some may last longer than others, even in the same conditions. That's why we check operation, right?
As one of the Glock instructors once opined in a class, fresh springs help keep guns alive. I wouldn't presume to gainsay him.
Ask for a replacement interval recommendation from any gun maker, and if you don't like the answer, ask again a year later.
In my first S&W armorer class (90's), we were told that for many years the company would randomly select and load magazines for their centerfire models sold to LE, and then date them and store them in a vault. They were randomly pulled out and test-fired at different yearly intervals, checking for function. I was told that the longest period of storage they'd checked, and observed normal feeding & functioning of the mag spring, was 10 years. They recommended checking the free length of service mag and recoil springs against new springs, and replacing them if a spring became shortened more than a certain number of coil windings (relative to the new spring). In subsequent classes they changed that recommendation to replacing service mag/recoil springs (left loaded all the time) every 5 years or every 5K rounds fired.
Recommendations by other gun companies might vary, or be left a bit vague (i.e. do it when it needs it, and hope that first symptom happens on a range, and not on the street).
I tend to look at it from the perspective of it being
my gun, and
my life that may be at risk.
