I don't believe Crosman ever made a model 40 rifle. I have no reverence to any model by that number made by Crosman. However they did make a model 140 from 1954 to 1968 in four variations.
1954 to 1968
need the actual serial number to determine the manufacture date of the rifle.
The manufacture date is when the rifle was made.
If you would post the serial number and model number,I can give you a date of manufacture.
date of manufacture, np=98 date of manufacture, np=98
your marlin rifle was made in 1957.
By it's serial number.Go to proofhouse.com to find the date of manufacture.
1984.
1967
1893
1883.
1985