In the older Journal article (#24) by Roy Jinks, he references Registered Magnums bought for agent distribution by the FBI. Roy cites that the 3 1/2 and 4 inch versions were the favorite bbl lengths that were purchased by agents. Roy writes, "Finally, in July of 1937, the F.B.I. purchased 100 units for issue to its force. These revolvers, registration numbers 2666-2765, had 5 inch barrels, Baughman quick-draw sights, . . . . .".
Why do you think the 5 inch was selected for presumed concealed carry, over the more conventional shorter barrel length? (Guess that this answeres why the FBI Commerative was produced with the 5" barrel).