Its an interesting discusion we are having hear, while I was taught not to drop the slide on a chambered round, and I haven't for the last 35 years, I believe that there is enough room in the extractor channel to allo the extractor to flex back with out causing any more spring set then when a round is chambered from the magazine.
Just resently I found a document by the US Army dated in 1914 that encourages the dropping of a cartridge into the chamber and dropping the slide, if you intend to carry in the ready with more then 7 round in your pistol, if you read page 13 under methodl of operation you will see that it is encouraged.
AUTOMATIC PISTOL, CALIBER .45
MODEL OF 1911
WITH RULES FOR MANAGEMENT. MEMORANDA OF
TRAJECTORY, AND DESCRIPTION
APRIL 1, 1912
REVISED FEBRUARY 14, 1914
GOVERNMENT PRINTING OFFICE
Office of the Chief of Ordnance,
Washington, February 14, 1914.
This Manual is published for the information and government of the Regular
Army and Organized Militia of the United States.
By order of the Secretary of War
Brigadier General, Chief of Ordnance,
METHOD OF OPERATION.
A loaded magazine is placed in the handle and the slide (3) drawn
fully back and released, thus bringing the first cartridge into the
chamber (if the slide is open, push down the slide stop (8) to let the
slide (3) go forward). The hammer (23) is thus cocked and the
pistol is ready for firing.
If it is desired to make the pistol ready for instant use and for
firing with the least possible delay the maximum number of shots,
draw back the slide (3), insert a cartridge by hand into the chamber
of the barrel (2), allow the slide (3) to close, then lock the slide
(3) and the cocked hammer (23) by pressing the safety lock (36)
upward, and insert a loaded magazine. The slide (3) and hammer
(23) being thus positively locked, the pistol may be carried safely at
full cock, and it is only necessary to press down the safety lock (36)
(which is located within easy reach of the thumb) when raising the
pistol to the firing position
shoot safe, shoot straight, and have fun