Help With A 1945-S Shell Case Lincoln Identification

A question please for anyone who's knowledgeable on the subject of "Shell Case Lincoln" pennies minted during the war from 1944 through 1946.

All research indicates these were composed of 95% copper 5% Zinc and weigh ~ 3.1 grams. Every picture I've seen of this year/mint combination clearly shows the coin as a copper colored specimen to varying degrees (depending on condition of course).

My question is this: While going through some of my steel penny rolls, I came across this 1945-S Lincoln that looks exactly like a steel cent except it's NOT Magnetic. According to my digital scale it weighs 3.15 grams.

This has me pretty baffled. Has anyone seen or heard of a 1945-S Lincoln that appears to be steel but isn't? It doesn't appear to be plated, as any plating would have at least partially worn through. I do see little hints of what appear to be copper in about three small areas of the obverse rim. This might have come from contact with a copper coin or it may be a clue to this coin's true lineage. This 1945-S (and the others in this roll) have been in my collection since around 1969 so I know it's history from that time on. All insight to help figure this riddle out is greatly appreciated.

And my apologies if the picture size/detail is lacking. This is my first go at uploading pictures to this coin community