I was a Viet era AF vet but not in that country. I was trained and issued a S&W Model 15 at the SASS site I was stationed to. After an Airman shot himself in the leg playing quickdraw at another site they took them away and issued M16-A1s as we were with an Army detachment instead of AF M-16s.
I later did carry my own S&W Model 19 on deployments with a Combat Comm. Gp. It was probally not 100% legal but my NCOIC knew and approved.