holy crap, ammo is expensive now

DON'T ENCOURAGE ME TO BUY MORE ARMAMENTS.

I mean, before you know it I'll be going out for bolos.

Practice. I shoot mainly pistol, though I'm branching out into rifle and shotgun, and don't own any pistols suitable for hunting (yet). But if you buy in bulk, it's much cheaper per round, and you have a hedge against ammo prices going up (more).

or something else which as a not-shooter I would never have thought of?

Well, it's not as if I have a large trough of ammunition in which I swim, ala Scrooge McDuck in his money bin.

Although... hmmmmmmm.

Partly to practice, partly to recreation. It's just plain fun to put metal downrange, and the bigger the gun, the more fun it is. This starts getting very expensive when you get a Class-3 or Destructive Devices permit... Mr. M134, for example, costs about $200 per *second* to fire.

Reloading is a very good option; while you have to keep buying new slugs, and need to inspect your spent brass carefully, it saves a lot on brass, and after a little experience, you'll be able to get much more consistent loads than you'll get from the factory.

And then, you get to the next phase, experimenting to find the best possible load for each weapon... which then leads to finding other ways to improve accuracy... and before long, you're making your own guns from billets. It's a slippery, but fun, slope. ;-)

Reloading consists of collecting the empty cartridge casings left after your day's shooting, cleaning and refurbishing them, and then putting new primers, powder, and bullets into the casings. It's the gun geek's version of recycling.

You can save a considerable amount of money this way, and you can also experiment with different loads. As rdfox notes, it's also possible to get results much more consistent than factory loading, which results in better accuracy.

OTOH, if you screw it up and put a double charge of powder in a round because you're not paying attention, you can blow up your gun. Some gun companies, Glock for one, state outright that firing anything but factory-loaded ammo voids your warranty.