Cartridge Stamped

I found a old cartridge stamped 38 a.c. need info?
I was going through some old cartridges in my dads gun case and found a old grimy looking cartridge stamped 38 a.c. I have never heard of one before. it looks like a rimless 38 special FMJ. I have never heard of a firearm chambered in this. is it obsolete? if so why?
.38 Auto Colt, used in older guns and then replaced by the .38 super. These are longer than .380 acp. Antique and pretty hard to find. Later the 9mm and .380 pretty much took over the market with better ballistics.
@ Eferrel – 9mm has more ft. lbs of energy than .38 acp.
9mm PARA = 320lbs. – 465lbs.
.38ACP = 312lbs. – 388lbs.
.380ACP = 189lbs. – 220lbs.
To break it down for you, I was saying those two calibers are more versitile, one more powerful and one less powerful, thus the extinction of the .38 ACP. LOL.