In 2" through 3" barrel 38Spls, my personal view is that the barrel/cylinder gap is best when tighter than normally seen, like down around .002" - .003". That will give you maximum velocity with any ammo; the very best 38+P defense loads are still marginal, and need every extra bit of boost they can get.
Small gaps equals more velocity. It's hard to get exact figures because nobody I know has taken a tight .002" gun and filed it out to .008" or whatever ("barely in spec") and measure with a crono before and after.
But as much as 50fps has been loosely reported, and that can mean the difference between hollowpoint expansion and failure.
For the record, my opinion on the best three loads for 38snubs:
1) Winchester 130grain Supreme 38+P. HUGE hollowpoint cavity...I doubt many autos could even feed something like that.
2) Speer Gold Dot 125grain 38+P - this projectile is loaded by Speer, Proload, Georgia Arms, Black Hills and probably other small shops (also available as a handload component). Gold Dot jackets are a heavy plating process, fairly thin but stuck to the lead particularly well.
3) The classic 158grain plain lead hollowpoint based on a semi-wadcutter "Keith type" profile, known as the "158 LSWC-HP+P". Federal's version is out of production and loaded wimpy - avoid. Winchester's is good and widely available; Remington's variant is supposedly just a hair hotter and not as easy to find...check gun shows or similar, if you can't find 'em the Winchesters are OK. Oh, and Cor-Bon used to load them and they had a GOOD rep for real heat - use in a modern gun in good shape ONLY and even then in moderation (same for the current 110 and 125+P JHPs).
I doubt those are the only good choices, but they're the ones I trust.