The NYPD Duty load for revolvers from the mid 1970's through at least the mid 1990's when they transitioned to autos was a 158 grain lead semi wadcutter (solid) loaded to +p pressure and velocity.
Stainless steel revolvers and speed loaders were adopted in the 1980s slowly replacing blued revolvers and the previously issued dump pouches for spare ammunition.
The Jay Pee holster was adopted nearly 100 years ago. It had a covered trigger guard used a thick lip of leather to catch the edge of the cylinder for retention. It, and it's loose belt were deliberately chosen in an era when even uniformed officers still wore their guns semi concealed, at least in the winter. Draw was done by placing your thumb between the gun and the lip and twisting. It was chosen for retention over speed of draw. The old NYPD guys who schooled me advised you should strive to see trouble coming and if in doubt, have your gun in hand.
Compared to it's contemporaries, the suicide strap border patrol holster and the clamshell, it was not a bad choice in its day, especially for the crowded conditions of NYC.
Many of its contemporaries required you to put your finger in the trigger guard and push a button or disengage a spring steel clip, the "serpa" of their day. Context matters.
The loose skinny belt, from an era of minimal equipment, also allowed many to rotate the gun up front to 1' o'clock in an "appendix" position. This was particularly useful sitting in vehicles. Yes, this was a thing long before the internet.
The pen and pencil holder versions of the Jay Pee were sorry, as were the swivel versions. Later versions of the Jay Pee were reinforced with two rivets at the rear and were made with better, thicker leather.
For better insight into the Jay Pee holster and it's use check out this thread by the late Pat Rogers on Lightfighter.
https://www.lightfighter.net/topic/o...-nypd-holsters