Not many slides, but a LOT of barrels and a lot of 4140 aircraft/rocket parts. I'd expect the steel case stuff to be on the order of A36 properties, which are about half of 4140, but MUCH easier to form and MUCH cheaper.
A36 will be in the low 20's on the Rockwell C scale (hardness), while 4140 is typically over twice that. A36 yield is 36 KSI (duh) vs 80 KSI for 4140, and A36 ultimate is 60 KSI vs 100 KSI for 4140.
This website has a good layman's description of the differences between A36 and 4140:
http://www.precisiongrinding.com/Plate/Steel_Plate/custom_steel_plates.htm