Hello.
38 Special LHP +P
Since the linked article above was written, I chronographed a newer batch of Remington factory loads. I cannot find a lot number, but the date "11/4/09" is on a flap. These figures were obtained within the last month and to the best of my memory, none of this ammunition is over 2 years old. ("Documentation" is not the best on the ammunition I admit, but the figures obtained were for me; just posted them here to try and help with the OP's request. Individual readers will make up their own minds whether it's for real or not or might feel it best to just ignore since it is not documented as per the scientific method; their choice entirely.)
Average velocities are based on 10 shots fired 10' from the chronograph screens.
Remington 158-gr. LHP +P:
S&W Model 642: 812 ft/sec
S&W Model 042: 828
S&W Model 638: 831
S&W Model 442: 820
S&W Model 642: 822 (This is a different Model 642.)
Average of these five S&W snubs ( 1 7/8" barrels): 823 ft/sec with this load.
Federal 158-gr. LHP +P: (Lot #K31P2)
S&W Model 642: 779 ft/sec
S&W Model 042: 786
S&W Model 638: 796
S&W Model 442: 781
S&W Model 642: 783 (This is a different Model 642.)
Average of these five S&W snubs (1 7/8" barrels): 785 ft/sec with this load.
Winchester 158-gr. LHP +P: (This ammunition was bought new about 2 years ago by a friend of mine who sold his .38's. It was not in the factory cardboard box but a plastic one so no lot number is available.)
S&W Model 642: 789 ft/sec
S&W Model 042: 810
S&W Model 638: 825
S&W Model 442: 814
S&W Model 642: 797 (This is a different Model 642.)
Average of these five S&W snubs (1 7/8" barrels): 807 ft/sec with this load.
I find the Remington the softest of the three and prefer it for use in the snubs. From a 3 or 4" barrel, I believe that any of the three will expand nicely.
I do not know the "why" of it, but have seen the Remington LHP's that appear to be "loaded out" a bit as described and pictured in a previous post and chronographed them. I found no practical differences in average 1 7/8" barrel velocities between the two, similar to expected shot-to-shot variations with the same ammunition fired from the same revolver. (The "loaded out" Remington LHP +P can be seen in some pictures via the link above.)
This is the stuff that can drive a person mad.
Best to all.