When I was on Lansing, Michigan PD in 1965, we were issued some type of “armor piercing” .38 Special ammo to be carried in every other chamber in our 6 shot Colt revolvers. If I remember correctly (and that is a crap shoot

), it was a fully metal jacketed pointed bullet. The other chambers were loaded with standard lead round nose.
I think the idea was to be a little more effective on car doors.
PS: We also carried ax handles instead of standard riot sticks.
That was a really cool department back then.
TJ