Actually Browning designed the 1911 with a near-square bottom firing pin stop.
The modified design found in today's 1911 FPS's is a little known change Browning made due to the complaints (by horse mounted soldiers that were carrying hammer down on an empty chamber) that it was too hard to rack a round to battery.
I use the EGW Oversized, Square Bottom Firing Pin Stop. EGW - Firing Pin Stop
They definatly produce the effect of delaying slide opening. (barrel unlocking
) I had a problem with my CCG 460 Rowland kit that exhibited evidence of firing pin drag in its contact with the primer. The firing pin imprint looked like a stretched out comma. It comes from the barrel dropping while the firing pin is still in contact with the primer. Instaling the EGW square bottomed FPS eliminated the smear. (I was already using the heavy duty firing pin spring that has the effect of rapidly returning the pin.)
From Guncrafters Industries
A square bottomed firing pin stop serves to slow down the opening time and reduce the slide speed when firing powerful loads in a 1911. This is due to the contact point between the hammer and firing pin stop being lowered. The principal of leverage applies and it now takes more force for the slide to overcome the hammer spring tension, thus the slide speed is reduced. This can also be a desirable feature in competition pistols where it allows the shooter to run a lighter weight recoil spring for lesser perceived recoil. Our firing pin stops are made to max. [sic] factory dimensions to prevent excessive extractor movement, an important feature for increased reliability and proper function, and the corners are radiused to eliminate stress fractures. Machined from 4340 Chrome-Moly steel and properly heat treated, this is one tough part.
The most effictive use of the FPS is to radius the sharp corner that contacts the hammer. This radius is minor but removes the 90º edge and replaces it with a 16th inch radius on 5-inch Government models, a .075 on Commanders with 18-pound recoil springs or a 1/16th on Commanders with 16-pound recoil springs and 1/10th to 1/8th inch radius on the Officer's Model.
An important part of this system is the use of the standard 23 pound mainspring.
Just another example of the brilliance of John Moses Browning!