when to switch springs between 50 and 25

I've been trying 4.5 gr WST for 50 yards and 3.8 WST for indoor 50 ft and 25 yard. Both with 200 gr swc. The jury is still out on the long line but the short line load is great. My question is with a 12 lb spring the gun functions with both but I'm worried it may be hard on the gun for the long line. How can I tell? I can't go any more than 12 lbs as the slide doesn't lock back every time with the light load....

I have a 50 yard load and a 25 yard load and two different springs per load. Sounds like you're asking the same question I was about to which is:  when is it appropriate to change springs? And how can I change springs that doesn't cause me and my actions to irritate other shooters or range officers (safety concerns)?

I don't think your two loads are significantly different in terms of gun wear.  I would worry about a different spring for a wadgun that I planned to put some true hardball through (230gr at 850fps+), but I wouldn't worry about the difference in 50 and 25yd loads.  I'm sure somebody must do it, but in all my years I don't think I've ever seen anyone regularly change springs during a match.  It's just not needed with bullseye loads. And it's an awkward activity on the line.

When I shoot my really light 3.3 gr BE loads for short line I change recoil springs or it won't function. I can change a spring in less than a minute. No different than swapping out .22 conversion to CF gun.
Jon