Just picked up an M48A. I took it to the range yesterday, got everything set up, loaded a round into the mag, closed the bolt, pulled the trigger, and CLICK, no bang. The primer didn't even have a dent in it. I tried again and the same thing happend, no bang, and no dent in the primer.

Any thoughts on this?

Weak or broken firing pin or pin spring, excessive cosmoline accumulated in the bolt assembly, wrong parts installed, incorrect assembly, etc.

Did this gun ever work?  

Does the cocking piece go forward forcefully when you pull the trigger?  

Does the cocking piece actually cock when you open the bolt?

Does the safety work right?

Try disassembling the bolt and check the parts.  The problem could be one (or more) of several things wrong.