Remington.com has a list
1981 I believe. http://www.remingtonsociety.com/rsa/questions/barrelcodes
Someone at the Remington Society of America should be able to help.
Only the 700 VLS is made in 6mm
100-400 USD
The serial number including the letter,or letters preceding the number must be included in your question to get an answer. Between 1962 and current date.