Pictures would help.
AMS stands for American Medicinal Spirits, a company formed by the Wathen family in Louisville to serve as a consolidation warehouse and medicinal whiskey seller during Prohibition. After Prohibition, AMS became the main component of National Distillers, one of the top U.S. spirits companies until it was acquired by Jim Beam Brands Co. in 1987. AMS ceased to exist as a company with the formation of National, though it's possible that National continued to use the name as a DBA for some products. As Straight Corn Whiskey, the product would have been aged for at least two years in either new uncharred or (more likely) used charred barrels (most likely barrels that previously held bourbon). Corn whiskey has never been a big seller and isn't something whiskey enthusiasts pay much attention to. Corn whiskey does not have to be aged so most of it isn't, making a straight corn a fairly rare item in any era.