OK you heathens, this is a very basic explanation as I learned it. Early GI model 1911's were made with a higher walled ejection port like the first photo. True replicas generally have this type of port. It worked (works) well and was/is reliable, with some caveats. It slings brass at your head/face every so often and it sometimes would ding the brass on ejection. The brass damage was typical and common, but not every gun did it, some only did it sometimes, etc. Similarly, if there was damage, it could range anywhere from a small ding in the side of the case all the way up to splitting and denting of the neck. When 1911's became popular with competition shooters and civilians that reloaded, lowering and flaring of the port was their solution. The higher wall was designed to keep crud out of the military firearm since it was generally on someones hip while crawling through all kinds of mud, sand, etc.
The second photo shows the more modern lower walled ejection port to fling brass more laterally and uniformly. The port is also flared at the rear of to prevent the dinging of brass.
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