I used to claim that I reloaded (and later cast bullets) to save money. But, about two decades ago, I was presented with the argument that I believe is more appropriate (and has been brought up by other posters):
I reload so that I can afford to shoot more.
Could I shoot if I stuck with factory ammo? Absolutely. ...But not much. The shooting budget is pretty limited. And I certainly would not have the wildcat, obsolete, and/or oddball cartridges that I mess with. Specialty stuff like that is extremely expensive to buy (or have custom loaded) - if it's available at all.
But by reloading, casting bullets, and swaging bullets, I have a much lower financial investment into the ammunition. As such, I can shoot a whole lot more for the money - especially with those aforementioned wildcats, oddballs, and obsolete cartridges.
Bullet casting (or swaging) is just a deeper dive into the reloading hobby. More cost savings (or more ammunition available for the money). More appreciation for doing more of the process yourself. And more ability to control the quality of yet another part of the equation.
I learned more about case design, chamber dimensions, and a bullet's behavior when being violently expelled from a barrel, by getting into cast bullets, than I ever thought I would care to learn. That, in turn, provides a better understanding of what's going on when working with other bullets, or even just trying to understand why certain bullets will or won't work in certain cartridges and/or firearms.
To me, the knowledge has been far more valuable than the cost savings. (Though, at this point, I don't know that I'm 'saving' any money, anyway, since I'm still buying equipment and molds all the time...)
Without bullet casting, I wouldn't have gotten to the point that I could pick up a wildcat, get some chamber dimensions, and draw up a bespoke bullet.
That's pretty much how I handle everything now, when I want a cast bullet. If NOE doesn't offer what I want and there aren't any open group buys that might work, I just draw up my own. If Mountain Molds can't cut my design, I send the drawing to Accurate Molds and have Tom cut it. (Each place has its own machining limitations, but Accurate can usually cut what Mountain Molds can't/won't.)
Mistakes have been made. My small pile of failed designs is lasting proof. But more knowledge was gained in the process.
...Some of my thoughts.
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I don't cast much for bottleneck rifle cartridges. I'm not entirely sure why. It's probably just laziness - not wanting to deal with dialing in a bullet/lube/sizing combination, since I have found some good jacketed bullets that do very well and I can't keep up with everything in the safe, anyway.
My molds are primarily for .32 caliber revolvers (primarily .32 S&W Long, .32 H&R, and .327 Federal), 9mm, and .44 caliber revolvers and rifles.
But there are some bottleneck exceptions: I have a nice assortment of molds for use in .30-30, 7.62x54R, and 7.7x58mm Jap (with some cross-over with the .32 revolver bullets). They could also be used in .30-06 and .30-40 Krag; but the bullets really correct for those applications. There are also a couple molds for .35 Whelen. And, I've purchased a few commercial molds and designed a few molds for .475 Tremor (with crossover with .480 Ruger).
I also have three or four commercial molds and one custom mold in .40, .41, and .43 caliber that are used strictly to cast pure lead bullets that I use as cores for swaged bullets. But, that's another topic in itself. (And, unless you go redneck like me, generally a very expensive one.)
I typically only buy molds with designs that have a gas check shank, and only design bullets with gas check shanks, now. It really isn't necessary with some of the cartridges/loads; but it makes my life easier. Instead of having to fiddle around and find out whether or not a particular bullet (or firearm) needs a gas check, I just run everything gas-checked. To me, the extra cost isn't a big deal and it doesn't really take any more time, since I size all bullets. (I don't shoot anything as-cast.)