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.
The manufacture date is when the rifle was made.
See http://www.fulton-armory.com/tea/m1serial.htm Oldguns.net. Scroll down the menu on the left to Manufacture Dates - US Military.
First variation has manual cocking and steel breech 1977-81 Second variations had plastic breech 1981-96 After that is was the 1377C model 1998 to present
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.
I believe you are reffering to th model 1903, bolt action rifle in 30.06 caliber. Value for these rifles is determined by overall condition, make, and date of manufacture. Date made can be determine by serial number and maker's name.........................
1984.
1987
1883.
1985