US cents were never made out of rifle casings themselves, but they were made from shell casings during 1944 and 1945. These coins were of course called "shell-casing cents".
In 1943 the Mint struck cents in plated steel to save copper for use in ammunition. The steel coins were unsatisfactory in almost every way - they were confused with dimes when new, after a while they either rusted or turned an ugly gray, they didn't always work in vending machines, etc., etc. As the war turned in favor of the Allies there was so much spent ammunition that the government was able to divert some of the scrap for use in coins, so starting in 1944 coinage of bronze cents resumed.
1815 is the only year U.S. one cent coins (pennies) were not made.
1860 The last copper pennies were made in England, and the same year the first bronze pennies were made.
These pennies are called "Wheat Pennies". They were last made in 1958.
1982
During WWII copper was needed for ammunition in the form of shell casings and bullet jackets. In 1943 the mint made cents from scrap steel to save as much copper as possible for the war effort.
The last year wheat cents were made was in 1958.
your serial number indicates that your Glenfield rifle was made in the year 1977.
For a specific answer, you need to ask about a specific year.
You can't answer this without knowing who made the rifle.
There are no exact records of the number of copper pennies made in 1943. It was about 40. Most pennies that year were made of steel.
1982
Pennies are made of zinc and other alloys with a copper coating, pennies made before 1964(or around this year) they were made of just copper. What you see on a penny is not rust but corrosion of the copper coating.