Could be the magazine, ammunition, dirt.
your winchester model 100 semi-auto rifle was made by winchester in 1962.
have you tried the Winchester web site
The Winchester Model 100 debuted in 1961 with the last one being produced in 1973.
your Winchester model 100 semi-auto was made in 1965.
the Winchester model 100 semi-auto rifle was made between 1961-1975.
A250644
http://www.jocoemprise.com/rifles/winchester/winchester100.html
With the serial number that you have supplied;your Winchester model 100 semi-auto rifle was made in the year 1963.
With the serial number that you have supplied,your Winchester model 100 was made in the year 1966.
The door jamb was made of wood. We painted the fireplace jamb black.
A jamb is the frame surrounding a window or a door.
Jellia Jamb was created in 1900.