Jungle Gun was a term used by one company ot designate a shotgun that had some sort of means to spin a solid projectile accurate ot over 100 yards ans shoot shot charges as well.
I cannot remember off the top of my head what company it was but H&H used Paradox, others used Cosmos, Collindon [sp] etc.
Westley Richards probably developed this principle further than the others wioth their very good sheels for their version. I know the 28 ga was called the Faunetta and their catalogue shows it killing game as large as moose.
There are a lot of jungles the world over, so I would want to know which jungle I would be in, before picking a suitable gun to carry.
A double rifle drilling would also be a good pick for most places I think.