I was still working when the S&W J-frame 357 Magnums came onstream, and wanted no part of owning or firing any of them. The J-frame 38 Specials were always popular as off-duty and back-up arms, even after we went to autopistols in 1987. I recall my initial reaction to the idea of J-frame 5-shot 357s, something along the line of "My thumb will be back near my elbow by Round 5".
Time went on, and eventually a rangemaster buddy talked me into shooting his all-S/S J-frame 357, with Pachmayr ComPacs installed. ALL RIGHT. 15 riounds, cylinder full and 2 HKS speed-loaders filled with Coin Of The Realm--WW Super-X 158 grain JHPs. First shot wasn't all that bad, but it darn sure wasn't pleasant. By Round 5 my thumb was still in its OEM location. 5 hits inside the 8-ring on the B-27 at 15 yards. Re-charge, and walk to the 10 yard line. 5 more, as before, about 2 seconds apart, 5 hits a little closer together. Re-fill and step to the 7 yard tile--all inside the 10 ring, carefully aimed, about 3 second intervals. ENOUGH.
My hand was SORE. On what planet was this sort of thing FUN? But I did check off "Shoot 357 Magnums from a J-frame revolver" from the Bucket List. My shop's current 357 carry load--the Federal #357B--is the FBI-blessed 125 grain JHP alleged to achieve 1450 FPS in 4" barrels. In my tight 686 x 4", these clock a true 1425-1430 FPS, so 'pretty close' to ad copy. My agency went this route because most 357s being carried were getting carried in 2"-3" revolvers, and the 158 grainers weren't expanding reliably from the short barrels and resulting reduced velocities. The Federal #357B bullets did open up in Jello. The 125s have noticeably less recoil in my 686 than the 158 grain loads did, FWIW. I imagine that reduced recoil happens in the J-frames as well, and so I think we have discerned the true/actual rationale for the load change. I won't tell if you won't.