Our own bmcgilvrey tested 2400 in a 38 SPL years back. He also tested other powders, but commented "It will be noted that the slower powders still register the highest velocities in the short barrel." 2400 and SR4756 beat out Herco and Unique.

I have not bothered to check but please note that his load is almost certainly above current recommended max loadings.

His results:

158 Grain Lead SWC/11.5 Grains 2400

2-inch Barrel
MV 1037 fps
ME 377 ft./lbs.
ES 71 fps
SD 30.2 fps

4-inch Barrel
MV 1150 fps
ME 464 ft./lbs.
ES 50 fps
SD 26.8

6-inch Barrel
MV 1162 fps
ME 474 ft./lbs.
ES 58 fps
SD 22.2 fps

8 3/8-inch Barrel
MV 1102 fps
ME 426 ft./lbs.
ES 67 fps
SD 24.0 fps

Google "Four High-Performance .38 Special Handloads" if you want to read more.