Dave - the issue round in 1991 was the Federal +P+ .38 Special 147 grain Hydra-Shok. Just prior to that the issue load was the famous "FBI round" - the 158 grain lead semi-wadcutter hollowpoint +P, in both the Remington and Winchester varieties.
Agents had to carry the issue .38 ammo. According to the regulations of the time, an Agent could carry Magnum ammo with the specific permission of the ASAC (Assistant Special Agent in Charge). The usual Magnum ammo was Winchester Silvertip (145 grain), though I have come across 158 JHP in gunvaults on occassion.
No revolvers are authorized for carry in today's Bureau. I don't know for sure what happened to all the Model 13s, but I suspect they were destroyed. Once I saw some desk sets that the Quantico gun vault was making up for visiting dignitary give-aways - they had the vertical foregrip from a Thompson submachinegun mounted on a base, with a Model 13 cylinder next to it for a pencil holder. Another time I requested a bunch of Simunitions guns for an exercise, and I got a case of Model 10s with Simuntions cylinders fitted to them. They had all been painted bright orange.