What's the intended use of the L-frame? Range fun? Defense? Both? Makes a huge difference on what and how to play with springs.
I disagree with those suggesting snipping rebound springs or bending mainsprings, though you can certainly alter your action to your liking that way -- just personal preference, I don't like damaging and possibly undermining the function of springs when a swap to a different, properly selected one can accomplish the same thing without risking performance.
I wouldn't shorten or loosen the strain screw, either, but some happily do.
How's the action of your piece as-is right now? If flawlessly smooth, great -- might be time for springs. If not, in my opinion you're better off leaving well enough alone or getting to where the action is flawlessly smooth because lightened springs will accentuate any flaws, particularly on rebound where the strength of the stock 18lb rebound spring drives through action hiccups; a lighter rebound spring will have more trouble and you'll notice it when shooting.
Each gun, even within the same model, has its own personality, and will respond differently to the same springs, so you have to experiment.
If this gun might see any defensive use, I'd stay with the stock mainspring poundage and use a Wolff. Wolff springs really are the best, and as noted earlier, are probably rebranded by Brownells and Wilson (I think this is confirmed for Brownells).
If this is just for range fun, consider a reduced poundage mainspring but you may experience light strikes; you'll have to experiment with ammo or with primers if you load your own. Federal are considered lightest.
S&W overcompensates a little -- and rightly so -- in mainspring and rebound spring poundages to counter for any factory hiccups in the action (burrs, tool or machine marks, etc.), or owner failure to clean and oil the internals and thus a gun that will have to function correctly when dirty or dry (or both) -- you name it. I don't mind easing off a little, poundage-wise, on that expectation because my revolvers are kept well-maintained.
All my guns stand the chance of being used defensively, so I stick with factory weight Wolff mainsprings, which nonetheless feel very slightly lighter than factory mainsprings -- either because they are, or (you see the theme here) they're smoother. Wolff advises staying with factory poundage for defensive use, too, for what it's worth, and I think they know their own product well enough to take the recommendation sincerely.
After that, experiment with rebound springs from 11lb to 16lb. You'll have to find the one that feels right to your hand, and balances with the mainspring weight, in the individual gun in which you're experimenting. Make sure you're getting proper trigger return or you risk short stroking when firing under speed and you don't want that.
As a rule, the smoother, better tuned your action, the lighter a rebound spring you can get away with, if that's to your liking.
Personally, I think there's nothing better than a well-tuned action in which all moving parts or the revolver are smooth and well-mated, combined with a Wolff standard power mainspring and 16lb rebound spring...maybe 15lb in some cases.
Used to be I'd go for the lightest rebound spring a particular gun could handle and still give relatively positive trigger reset -- all about getting that lighter trigger pull. Smooth, too, to be sure, but I really wanted lighter. I've worked actions smooth to where they had excellent trigger reset with as low as 13lb rebound springs, and thought it ideal.
No so much, anymore. I let the action work handle the "lightness" factor, which is really a "smoothness" factor; the Wolff parts are very gentle icing on the cake while retaining a crispness to pull and deliberateness of reset I didn't fully appreciate before.
