Have you tested how often their guns jam? From what I remember there was a certain condition threshold for jams which was influenced by dirt and heat (if enabled in JA2-Options.ini). Above the threshold the gun would never jam. Below the threshold the gun was increasingly likely to jam. I wonder if the condition of enemy guns is good enough to not make them jam too often.
I know from a player perspective they can't jam "too often". ;-) From a balancing perspective I tend to disagree.