I liked the 13 as well. (Thought that I had to sell it to justify buying the 19 - now that I am older and have a bit more money, I kick myself for getting rid of it, but it was a different time and a different financial situation.) As you say, the shroud is a wash as to impaired function. I had not thought about the mud-filling idea, only the bending, which leads to the Colts - I always wondered why they were designed with the rod completely naked on the end, just looking for something to catch on.
Good point about Colts. But the geometry of the ejector rod's position, in relation to the barrel and frame, tends to offer it a great deal of protection all by itself.
