It's been discussed on here many times, it was assumed that EX stood for Exhibition rather than Experimental. What is 'Experimental' about it?
The woodwork has been butchered on the left side of the receiver.
It's a basic Number 4 with an unusual serial number, that's all, IMHO and certainly not worth what is being asked for it, hence it hasn't sold in years of being advertised.
https://www.milsurps.com/showthread.php?t=31316