My Dad was a Fed and he too carried a M66 2 1/2" RB and the issued load was the Winchester & Federal +P+ 38 Special. On several occasions they were authorized to load their Magnums, but for the most part carried the +P+'s. Heck, I still have a few boxes of the stuff but have never been a fan.

At least they did have the option if a ".357 Magnum situation" arose.