The short answer is the 30 GT was only made in 1979 and 1980. I understand the straight stock was unpopular vs the curved one that they discontinued it in 1980 after less than 8000 units were made.
The 1980 version should have an inlay of the state of Texas. (GT stood for Grand Texan) I own a 1979 version that is only about 200 units older than yours.
1975
manufactured 1970
Yes.
Then it was manufactured before January 1, 1969, when serial numbers were not required on long arms manufactured in the US.
THIS Glenfield MOD 50 BOLT ACTION SHOTGUN WAS MANUFACTURED 1966-1972. I HAVE ONE AND ALSO CANNOT LOCATE THE SERIAL NUMBER.
With the serial number provided,your Glenfield model 60 was made in the year 1973.
Your serial number indicates that your Glenfield model 60 was made in the year 1974.
Your serial number indicates that your Glenfield model 20 bolt action was made in the year 1980.
With the serial number that you have supplied,your Glenfield rifle was made in the year 1973.
your serial number indicates that your Glenfield rifle was made in the year 1977.
Your serial number indicates that your Glenfield model 25 was made in the year 1976.
The serial number on a Glenfield model 20 is located on the left side right behind the barrel on the outside of the breech.