How feasible is it to moonlight at a civilian institution as a pathologist while you're active duty?
The specifics of FP practice make it far less feasible (though not impossible) to moonlight as an FP than to moonlight as a general pathologist.
A. ME offices are (in most cases) state or local governmental entities so any moonlighting contract will have to go through governmental approval channels.
B. ME offices generally start the day around 0600 with cutting starting at 0700 and done by 1200. The rest of the day for the FPs is admin, report dictating, slide work (if necessary), scene investigations (if necessary), odds and ends (depositions, trial prep with prosecutors, meeting with families to explain how 6-MAM was found in their daughter's blood even though she was an angel and would never touch drugs, etc.), and tying up loose ends. Thus there's no way to pop over to the ME office after the duty day to do a little moonlighting. Weekend moonlighting would be feasible for the FPs stationed at Dover as long as they're not on call, but it's a different story for the FPs stationed away from Dover. Those military FPs are generally expected to be on call (including weekends) whenever not on leave to cover regional forensic autopsies so that Dover doesn't have to fly a team out to NAS Whidbey Island for a forensic autopsy on a Saturday morning when that autopsy could be done by the military FP stationed at Fort Lewis. Kind of tough to cover a weekend for a local ME office when you could be getting a call from OAFME expecting you to do a forensic autopsy on the Olympic Pennisula on Saturday morning.
C. The services between them generally try to have an FP stationed in the pacific rim and Europe to serve as a regional FP so that a team from Dover doesn't have to fly out every time a LCpl decides to play chicken with a lamppost while doing 100+ on his new Hayabusa. Not many opportunities for the Navy FP stationed at Oki or the Army FP stationed at Landstuhl to moonlight.
D. As mentioned above. You never know as an FP which case is going to go to trial. ME offices are loath hire a military FP to cover for the weekend when there's the possibility that if the case goes to trial the FP who signed out the autopsy wouldn't be able to take the stand because he couldn't take leave or was deployed.
The one military FP I knew who did moonlight was a go-getter who was not staying in the military past his commitment and was very aware of how the low numbers of forensic autopsies for military FPs were perceived on the outside. He found a small (3 man) ME office that was desperate for coverage about 500 miles from where we were stationed and would use leave to take a 4 day once a month to cover for that office. He flew in Thursday evening and cut Friday, Saturday, and Sunday with the understanding that one of the FPs would be in town and able to be called in for any homicides. Subsequently the office would FedEx tox results and other required studies to him so he could write his final report which he FedEx'd back to the ME office. If a case ever went to trial, he was on the hook to testify. The whole process was obviously a huge pain for him, but it allowed him to keep his numbers up and he had no problems getting an FP job when he ETS'd.