The RemingtonModel 121 fieldmaster was introduce in 1936 and discontinued in 1954
Request an owner's manual from Remington on their web site, it's free.
All 121's are date code, see related links for the table/information for looking it up.
Check date code on barrel - see related links
June, 1948
remington 740 fieldmaster . 30-06 caliber rifle
1949 - there is a date code on the barrel for month/year details on the Remington Society of Amerca here: http://remingtonsociety.com/rsa/questions/barrelcodes
It says it on the barrel, otherwise if there's no riffling it's been modified or shot out, but quite unlikely.
When was the serial? They all have serials. They were made from 1936-54 and have date code stamps on the barrel which can be looked up on the manufacture date link on the Remington Society of America.
Winchester didn't make it, Remington did. Worth 222-350 depending on condition and lust level of buyer
1946, it will be date code (month/year - letters) on the left side of the barrel. You can look this up under the manufactured date on the Remington Society of America site.
50-150 usd