How can I make more realism more fun?

Also Henry, I like tying ammo to jingle, since the two are virtually interchangeable. So, you need some barter huh? Well, if you swap out some your prize automatic ammo for cheap shit, you could scrounge up 1-Barter, but your Ornate semi-automatic handgun is gonna be at -1harm until you replace the ammo with some topshelf bullets.

As others have suggested, any 7-9 or miss in an aggro or sieze by force move leads to ammo issues. Clatter: failed Sieze by force (Joe's girl's Life)....
Hmmmm, you blow Joe's Girl's ear clean off with that last shot, despite taking a stab in the guts from her butcher's hatchet. Huh. You grunt in pain and land with an oooffff in the muck. Your waistbelt saves your skin, but your bandolier is leaking gunpowder all over the shop. Joe's Girl's riposte has opened up most of your shotgun shells, its useless without ammo til you scrounge some more.

How can I make potentially punishing realism more fun for my players?  This could go for any number of things, but I've been thinking about all of the ammo that people have been shooting for the past n-years since the world went to shit.

In general terms, look at the genre and see how they do it. Specifically, use it to heighten the excitement.

When Mad Max's shotgun fires on a dead shell its either followed by a fist fight or it causes everyone to gasp and hope he's got a good round in the other barrel when he cocks the hammer back. Alternately it suddenly deflates the tension when you realize he's just fucking with someone and wasn't really going to shoot them (although that's more PC side).

When Mal Reynolds is in a standoff with someone, pulls the trigger and is out of ammo there's always a pause for that oh crap moment then he dives for cover.

In more game-style terms, when the PC fails a roll and you think a jam is a good idea, make sure its an oh crap moment rather than just a you're wasted moment.

Well, zoph, that's not really realism, is it? That's genre fidelity.

I propose that realism actually isn't fun because if it were then we'd all just, like, be doing real life stuff instead of playing roleplaying games about brain exploding dominatrixes and resurrection-capable combat medics with special hugging abilities.

I was focusing on the fun part. I suppose my point was more: make more realism more fun by only using more realism when it'll be more fun.