Sounds about right FB2. A casing falling from, say, 10,000 feet, should reach terminal velocity at approximately 120mph. However, this would, of course, depend on it's actual 'flight attitude' during the descent; if stable, it would approximate the above speed. If tumbling, it would probably exceed that speed but, in certain attitudes, it could well 'float', therefore descending at a much slower velocity, but still fast enough to do damage, however small, to structures, and certainly to humans. This would be true of a rifle-calibre casings, such as .303 or .30 calbre, and more so with a .50 cal or cannon casing such as 20mm.
Although I don't know positively of any fatalities caused by falling cases, I have heard of injuries being caused, and I have actually seen evidence of structural damage, albeit minor, to a building.
Up until the late 1960's, there was a building on the banks of the River Tyne, at Newcastle upon Tyne, in the north east of England, that still bore the patches, on its corrugated metal roof, where the holes caused by falling .303 cartridge cases had been repaired. A friends father had witnessed the damage as it occured, during I think September 1940, when Spitfires intercepted a Luftwaffe daylight raid on the warehouses, and, I believe, what was then a Vickers armaments factory, that ranged along the banks of the river. The falling cases from at least one of the Spitfires were seen to shower down in a stream, as related by my friends father, some splashing into the river, whilst a fairly high number hammered through the 'tin roof'.
I have no reason to doubt this account, having seen the evidence with my own eyes. There used to be a small boat moored near this particular building, which bore the legend 'Wreck' in large, warning letters, which, allegedly, marked the spot where the (remains of the) bomber, I think a Dornier 17, had 'gone in'. This 'local folklore' tale was reinforced, IIRC, in the late 1970's, when some, I think, 250kg German bombs were recovered from the river.
I hope this has proved interesting, and gone some way to answer your original question.
Terry.