Beat me to it!
I was going to post this same question today. I, too, picked up some Federal 158 gr. +p LSWCHP (38G) last year, and have been wondering about it, myself. It really is very hard to find actual data on this load. It appears to do alright velocity-wise in
one recent test by BreakerDan over at the Smith & Wesson forum. 799 fps. out of a 2" barrel seems about the same as the 800 fps. that Steven A. Camp over at hipowersandhandguns.com gets out of the
Remington load (although in
another test he got better-than-usual results from it). BreakerDan's 4" results fall around 30 fps. shy of Winchester's claimed velocity for their version, so extrapolate away to guess at the 2" comparison.
Since the 38G seems to have been a Law Enforcement Only load before being discontinued entirely, is is possible this ammunition was made available from a run produced for a law enforcement customer, and would have the 'proper' powder charge?
Personally my curiosity has been about about the lead Federal uses. The Remington is renown for its readily-expanding soft lead. The Winchester is harder, working fine out of a 4" barrel, but only opening up a little out of the 2" pipe. How does the Federal stack up in this regard?