I'm with Norvic. We don't need instant ammo. Folks, it's a gun. It uses ammo. If you run out, you RUN OUT. When I was leveling range in real life (taking a .22 bolt-action to the local dump to plink cans, bottles, rats etc) I always brought at LEAST 3 boxes (150 rounds) with me. When hunting, my ammo load was 2 magazines (6 rounds) plus 12 more loose of .22-250. Guess what? I never ran out of ammo while hunting. Actually, I almost never broke into the loose rounds, but better to have 'em than find myself out, yes?
The easy way to handle the logistics of leveling: Turn one or more guildies into pack mules. I went out just last night with my bowrifle. 1700 rounds on my person, and another 1200 on my guildmate. That'll last a while. Even with me being the DD (she was working afflictions) it was enough for me to go from 145 to 148, and have 800 rounds left when things broke up. For launchers, get your "mule" to carry mats for you. 400 mats is 100 shots, and you can probably carry that between your own bit of space and your friend.
Launcher ammo needs a big improvement in effectiveness:bulk ratio, either making it smaller, making it hurt more, or some of both. Autolauncher might too, but I haven't played with it enough to say. Personally I'd like to see the damage come up more than I'd like to see the bulk go down, just from the "logic" of it being a bloody rocket launcher

I'll pay the PITA cost of levelling it for a good whack that makes hostile nukers duck and spread out.
Bowrifle/bowpistol ammo needs a reason to exist, as it has none right now. Bigger ammo that's more mat intensive to craft, and yields no improvement over rifle/pistol ammo? Err, yeah... Perhaps giving bow-weapons a range kick (say, +5 for pistol, +10 for rifle) and maybe 15-20%ish more damage would make it worthwhile, assuming that bow weapons become non-compatible with vanilla guns. Think of bowweapons as the "heavy" version. As a RL example, compare a .22 rifle to a .30-06. Both will shoot as fast as you can work the bolt, but the .30-06 hurts more and reaches farther, at the cost of heavier and bulkier ammo, and a heavier and bulkier gun. Continuing that theme, the rifle (.22) is what you level on, and the bowrifle (.30-06) is what you kill with.
Also, I have to agree that the fact you don't see many folk using it says something. Amitst could have left the troll comment out, though

Most people pick it up after they have something else at a nice high level. It DOES need tweaking.
As far as the craft aspect being a barrier, well, either you're a crafter or you aren't. I don't like digging much (I have 4 different combat skills that are higher than my dig, 2 of them by a LOT) but range actually gave me a reason to do it. And if you have a high dig skill from crafting something else, you can level range craft like crazy with all those mats you can pull. Once you get to a halfassed level, pumping out ten thousand rounds (2 full packers) isn't that much work.