These .357 magnum chrono results are from a 4" GP100, a 3 1/16" SP101, and a < 2" LCR. All Rugers. They are 5 shot averages.
Just for grins I'm also posting .38 Special +P load velocities for factory loads out of the LCR and using the same bullets.
.357 magnum loads are the Remington Express and UMC 125 grain SJHP and the Speer 125 grain Gold Dot JHP.
.38 +P loads are the UMC 125 grain SJHP and the Speer Gold Dot 125 grain Gold Dot JHP. Comparing the cartridges side by side, they appear to be the same bullets.
I have discovered that chronographing these loads on a 90 degree F day, and the same loads on a 55 degree F day, give different results. I had never thought about it before. I discovered it months apart naturally, as they occurred in different seasons.
So where I have readings for a load at both temperatures, I'm giving it. Some loads I only have at one temperature.
Anyway.............
.357 Magnum loads........
Remington Express 125 grain SJHP .357 magnum
GP100 4" - 90 degrees -1451 fps - 587 ft/lbs ME
GP100 4" - 55 degrees -1375 fps - 528 ft/lbs ME
SP101 3" - 90 degrees - 1375 fps - 528 ft/lbs ME
SP101 3" - 55 degrees - 1322 fps - 488 ft/lbs ME
LCR <2" - 55 degrees -1245 fps - 432 ft/lbs ME
UMC 125 grain SJHP .357 magnum
GP100 4" - 55 degrees -1384 fps - 534 ft/lbs ME
SP101 3" - 90 degrees - 1367 fps - 521 ft/lbs ME
SP101 3" - 55 degrees - 1334 fps - 497 ft/lbs ME
LCR <2" - not tested
Speer Gold Dot 125 grain .357 magnum
GP100 4" - 55 degrees -1348 fps - 507 ft/lbs ME
SP101 3" - 55 degrees - 1333 fps - 496 ft/lbs ME
LCR <2" - 55 degrees -1210 fps - 409 ft/lbs ME
Equivalent .38 Special +P loads............
UMC 125 grain SJHP .38 Spcl. +P
LCR <2" - temp not noted -910 fps - 231 ft/lbs ME
Speer Gold Dot 125 grain JHP .38 Spcl. +P
LCR <2" - temp not noted -869 fps - 211 ft/lbs ME
As you can see, the Express and UMC loads perform about the same. The Express load is in a nickled case, which can help extraction, and burns cleaner with less flash.
You can buy the Express load in 50 round boxes, but have to shop for it. It is only produced on occasion, so sometimes the online retailers are backordered.
I carry the 125 grain Express load in all my .357s, but carry the Speer Gold Dots in speed strips for reloads. They have no exposed lead like the Remingtons, and feed into the cylinder a little easier.
Lastly, these light revolvers, especially the LCR, recoil savagely with the magnum loads. I worry about a bullet walking out of the case and tying up the cylinder. I've never had it happen to me, but have heard of it happening to others.
When I ordered 500 of the Express loads, and 500 of the Speer Gold Dots, I immediately dumped them out and ran each round into the crimping die of my .357 mag die set. I used the best looking round as a model. Gave me peace of mind, and only took a couple of hours on my old RCBS Jr. press. Did it all during one 2 hours TV movie. I also did this for the UMC loads I bought at WM.
I love the .357 magnum, even in short barrels. They perform much better than most suspect.
I do hope I never have to touch one off inside a building, though.