Is it mainly ergonomics?
(Nice Pics BTW)
browning hi power and 1911 both designed by browning.
hi power handles the 9mm and currently also the .40s&w...the 1911 can handle larger rounds, the .45ACP, .38super and .10mm (bren).....
you can chamber the less powerful rounds for the 1911 but not visa versa....
the hi-power has a 14 round mag and the 1911 in .45 has a capacity of 7(or 8)
the 1911 has a govt mandated grip safety, the browning HP does not.
these guns are very similar single action auto loaders both internally and externally, both designed by the genius that was John Moses Browning
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A standard size Hi-Power frame is too light for a 45 ACP or similar load. Some of the first 10mm models developed frame cracks, and in subsequent builds they beefed up the frame in the affected areas without changing the external dimensions. If you wanted to build a Hi-Power in 45, you'd have to design the frame from scratch and it would be a little bigger and a little heavier. I think some eastern bloc gun maker did one.
No grip safety, obviously.
Pivoting trigger, instead of sliding.
Some Hi-Powers have this stupid mag safety that won't fire unless there's a mag in the well. Not sure what that's for.
Browning's later work, so he may have done things in a way he preferred to the 1911, but I don't know that for a fact. I believe I had heard it was one of his favorite designs.