I wanted to weigh in on the earlier thread re .40 adoption by the FBI, but it was closed, so here goes. I was a Special Agent trainee in the academy when the Miami shoot out occurred. Policy re .357 ammo at the time I went to the field after graduation in June '86, was that you carried .38 +P (Winchester 158 gr LSWCHP was issued to me) in the gun, but were authorized to carry .357 as your reload in your belt pouch or speed loader (Winchester .357 145 gr Silvertip was the issue .357 round at that time). Magnum ammo could be carried in the gun with approval of your SAC in extraordinary circumstances. Every FBI vehicle was supposed to have a box of .38 duty ammo in the glove compartment. I normally carried +P in my personal S&W Model 66 3" with .357 ammo as reloads.
Very interesting SOP. Glad we have advanced them over the years! Hell I have 2 33rd Glock 9mm mags in my center console alone!!
What was the reasoning given for the 38 load to start and the more potent as a reload?
Easier for most agents to shoot the .38’s well I assume. All qualification was done with .38 ammo, but you could draw and shoot as much .357 ammo as you wanted during qualification days. I always figured that if the first 6 didn’t have any effect, I wanted/needed a little more oomph to get the job done.
The .38spl is easier to shoot because of lighter recoil, less muzzle blast, and less muzzle flash. Also, just like the .357sig wears out auto pistols faster, so too does the .357mag in a revolver. Cracked frames and cylinder timing issues were common problems in agencies that used a lot of .357mag. Shooters today just don’t shoot revolvers as much as agencies did in the old days to experience these problems with high round count magnum loads.
Very interesting! Thanks for sharing your experience 
Seems pretty silly/dumb/risky/??? to make you use an entire cylinder of .38 (or at the very least, waste time unloading it all) before being able to decide if you need .357 
You’d think if they were OK with .357 at all they’d let you load it to start with.
It seems I recall the .38 spl. 158 gr. LSWCHP actually performed rather well in ternminal ballistic testing–better than most .357 offerings in 1986, if not all, and better than the 9mm 115 gr. W-W silvertip used by SA Dove. Perhaps I am wrong, but that is what I recall.
I believe the Canadian Police Research Centre (CPRC) used the .38 spl. 158 gr. LSWCHP round as its baseline in a 1995 study, and it met terminal ballistic protocols.
http://www.cprc.org/tr/tr-1995-01.pdf#search="Winchester%20gelatin%20ballistics"
This site is down from 2/10 - 2/14/2012 for maintenance; so, I was uanble to access it.
This link works!
http://publications.gc.ca/collections/collection_2008/ps-sp/PS63-2-1995-1E.pdf
It’s the government, it doesn’t have to make sense. I also learned rather quickly that the further away you were from D.C., the less strictly some of the rules were observed.
I have the forensic analysis completed by W. French Andersen regarding '86 Miami FBI Shootout with Platt and Maddox. Very good read overall.