Hi,
Seeing what prompts the question, there is a more complicated answer that I will try to boil down to it's basics. You bring up a very interesting question.
To start with in 1938, the coins looked great. Lots of strong detail on the obverse and reverses of the nickels minted for those years. The master hub was new and the master die(s) made from those first year hubs looked great. Consequently in the next step, working hubs and dies also were very crisp and full of nice detail.
That being said, the alloy used for our five-cent coins is extremely hard and wears out dies pretty badly. We see a lot of the effects of what is known as "
Die Deterioration" on nickel coinage. So with a particular years dies, the more the working die is used, the more worn the details get, the worse the coins look later in the run of the production for that working die.
That means that early strikes of a specific die in a given year can look great while later strikes have weak details.
The next issue to come into play goes back to the master hubs. Each year, they were brought out and changed with respect to the dates and in some cases other details. Generally though, each years subsequent use of the master hubs would wear them out. Progressively, year by year, the working hubs and dies would look worse and worse. They would be used to strike coins that as a result looked weaker and weaker in details.
This part is just a guess but I am going to attempt to place a date range on this by what I've seen on nickels. If someone has a more specific date range, please fill in the blank:-)
Anyway, In my experience, I would suspect that the master hubs were reused from 1938 thru 1957 as the coins details got progressively worse year by year. If you think the 1946 S looks mushy, you should see nickels from 1953, 1954 and 1955:-)
Again, this part is an estimate as I have no knowledge of anything specific, but it seems to me that something was done for production of nickels in 1958 as the details particularly on the 1958 Philadelphia nickels looked great.
I can't tell you specifics as to years where the master hubs may have been new or touched up in the 1930s, '40s or '50s but generally, what I outlined is the reason for the mushiness of the nickel coins as the series went on.
The 1946 S that was asked about is very typical for the year.
I hope this adds a little more to the discussion.
Thanks,
Bill