Autoloading rimfire rifle made around 3/4 of a million of them from 1941-1970.
If you can make out the letters on the left side of the barrel in front of receiver you should be able to date it from Manufacture Dates link on home page.
Needless to say taking steel wool to it, isn't going to hurt the value.
Found Gun
Re: Found Gun
it looks like a grooved receiver. If so, it was made in 1951 or later.