Jim:
Unless I’m mistaken, 1:50,000 scale maps are military only. Civilian topo maps in the US (produced by the USGS) are 1:24,000 scale. If there are any 15 minute quadrangle maps still available they are 1:62,500 scale. Neither are compatible with military grid readers or scales.
Here is a source for map scales and protractors available in a variety of scales – print or copy them on transparent material and have at it.
Regards, – Flighter