by serial no
They were made from 1967-1987 and are date code stamped. See related links for details how to look up the manufactured date.
Check the date code stamps on the barrel. Details on the Remington Society of America on the Manufactured Date link.
http://www.histandard.info/PDF/Sears%20Rifles.pdf The model 25 will have a two letter assembly date code onteh barrel.
Date code on barrel, check Remington Society of America - manufactured date link.
The manufacture date on the gun itself is WTT. The W indicates the month of August and the TT indicates the year of 1948. Hence August 1948 is the date your model 511 was born.
1930, will be date code stamped see related links.
1928, will be date code stamped on barrel, see related links.
1922 - will be date code stamped on the barrel, see related links.
1926 - it will be date code stamped on the barrel, see related links. Thanks I found the date codes.
Made 1993-1998 Check the date code stamped on the barrel. Look for the manufactured date link on the Remington Society of America for details.
It was made in 1918, so it won't be date code stamped and I also suspect not marked model 12 on the side.