As a retired detective sergeant and a former police training instructor, I can assure you that it is not necessary to field strip police automatic pistols to unload them fully. There are TWO steps which MUST be taken — done in the SAME order every time — as follows:
(1) Remove the supply of ammunition: take out the magazine, AND THEN,
(2) Empty the chamber of the last round. Lock the slide open and look down through the gun to verify the magazine is indeed fully removed.
If you do this backwards, you will RELOAD the chamber and WRONGLY believe you have unloaded the gun. YOU HAVE JUST LOADED THE CHAMBER AGAIN if done in reverse order.
This is not only the procedure to empty your own carry gun, but ALSO the procedure to unload the auto pistols you seize in making arrests, handling evidence, etc.
I can just imagine thinking you have to field strip an auto pistol in the field on the trunk lid of your patrol car every time you seize one in making arrests; you will have gun parts rolling off the trunk into the street.
REMOVE THE MAGAZINE FIRST. THEN EMPTY THE CHAMBER NEXT. Lock the slide open on an empty gun to prove your work.