Was snooping around as I am going to scratch an old Colt Revolver itch and found this which might be of interest to you guys.


From the Colt Model Guide:

Following World War Two, Colt assigned letter codes to all frame sizes. Even though a pre-War and post-War Colt's may have the same frame, only the post-War models were given letter codes. Technically, calling a pre-War Detective Special a "D" frame is incorrect. However, to avoid confusion it's common to call all Colt small size frames "D" frames whether made before or after WWII as is calling pre-war medium frames "E" frame models.

The Police Positive Special "D" frame was Colt's primary small frame used up until the end of production in 1995.
It had a longer frame and cylinder for use with longer cartridges like the .38 Special. It was used for:
Police Positive Special.
Detective Special.
Commando Special
Cobra.
Agent.
Diamondback.
Police Positive MK V.
Viper.
Courier.

The Army Special/Official Police "E" frame was Colt's medium frame as used for all Colt medium framed revolvers from 1908 to 1969. The firing pin was mounted on the hammer. It was used for:
Army Special.
Official Police.
Officer's Models.
.38 Special and .22 Trooper.
First Model Border Patrol.
Heavily modified as the Camp Perry Single Shot.
US Colt Commando
Marshall.

The "I" frame was essentially the "E" frame only with the firing pin mounted inside the frame. It was used for:
The 357 Model.
Later .38 Special and .357 Magnum Trooper.
Python.

NOTE: Due to the similarity of the Colt "E" frame and the "I" frame, these are usually just referred to as the "E&I" frame models.

The "J" frame was the new transfer bar safety-ignition system medium frame introduced in 1969 as a replacement for most of the older medium frame "E&I" models.
Models were:
Trooper Mark III.
Lawman Mark III.
Metropolitan Police.
Official Police Mark III.
Officer's Model Match Mark III.

The "V" frame was a slightly modified Mark III action. Models were:
Trooper Mark V.
Lawman Mark V.
Peacekeeper.
Boa.
Air Marshall.
Whitetailer.

The "AA" frame was a slightly modified Mark V frame made as:
King Cobra.
Grizzly.
Whitetailer II.
Combat Cobra.

The New Service frame was used for:
New Service.
New Service Target
Shooting Master.
US Model 1909.
US Model 1917.

The "MM" frame was Colt's first large frame since the New Service was discontinued in 1942. This was used for the Anaconda.

The "SF" frame was Colt's new small frame made of stainless steel with a transfer bar action. It was made as:
The Colt SF-VI.
DS-II.
Magnum Carry

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CAJ, the pre-war Police Positive had a couple frame sizes..I have a 1920 PP in .32 long it's a little bitty dude! maybe the bad guys were smaller then...they use diff. grips also...Colt's is a study all its own..I love them also!

Great reference material. Thanks for posting!