Casters generally come in two types: slings and rails. Both are designed to fire some sort of small projectile at high speeds with relatively good precision (depending on the caster). Like any weapon, they come in a large number of configurations and styles with an equal breadth of quality. Generally, the configurations can be divided into two main styles, Handcasters and Longcasters, while the type of casters are divided into Slings and Rails.

Handcasters are smaller and can be fired by a single hand. They are generally affixed to the hip or hidden beneath clothes. They normally contain only a few bolts (often only one) and are usually considered more of a defensive weapon. Many don't have sights and aren't very accurate beyond a dozen paces. They require relatively little energy, and thus can be fired quickly, but lack "punch" or penetrative power.

Longcasters are larger and require two hands to fire. They're considerably more expensive, but also much more powerful and accurate. They often have much higher energy requirements which can take as much as half a minute to charge. For this reason, they tend to have a larger reservoir followed by a trigger reservoir, which feeds into the main reservoir, causing it to "trigger" it's release, firing the bolt. While Longcasters aren't restricted, neither are they generally available to the public, mostly because a good Longcaster can cost half as much as a decent home. Richer merchants and Royals tend to prefer them, often for hunting game.

Slings

Slings are the most common caster by far. They're simple devices that have a reservoir, a chamber, a sling, and a barrel. Generally, someone will place a bolt, usually something dense but cheap, in the chamber, which sits in front of the sling. They then feed graescence into the reservoir, which builds up a charge. Once it gets full, it releases its stored energy into the chamber, which causes the sling to propel forward along tracks in the bottom of the barrel, slinging the bolt out ahead of it at... some speed. There's trade off between reservoir size, which takes time to fill, efficiency, and the speed of the sling.

There are innumerable variations, including pre-fill reservoirs, multiple reservoirs, partial discharge reservoirs (sometimes paired with some form of ammunition feeder), etc. Lower end casters can sling just about anything that'll fit down the barrel. Higher end slings, though, will require custom ammunition. These often included rifled barrels and are highly accurate.

Rails

Rails are slings without the sling. The basic design is the same except instead of using a sling, the bolt itself is propelled directly. For that to happen, the bolt needs a core to react to the graescence. Most modern day rail casters use a single core— really just a sliver —and spiralled rails to spin the bolt.

Rails have several distinct advantages over slings: they are extremely efficient, have no moving parts and thus more reliable, can propel a bolt at many times the speed of a sling, and are far, far more accurate. They don't suffer as much from the delays inherent to slings and can punch through just about anything with the indestructible ammunition core.

They're also the equivalent of firing money at your enemy. Even Royals blanch at the cost, and so almost nobody uses them. That isn't to say Royals don't own them— Railcasters are a fantastic statement of money and power —they just don't use them all that often, preferring a more sane method of conflict resolution that doesn't require one to empty one's pocket just to get some satisfaction... like duels. Royals love duels.

Railcasters otherwise tend to be limited to high grade military weapons, and here is where they get interesting.

Perhaps the most common variant is the two-stage Snipercaster. A type of Longcaster, it contains two sets of staggered rails— one spiralled, the other straight —fed by independent reservoirs. This helps compensate for the loss of momentum inherent in using spiralled rails. A high end Snipercaster can hit a single leaf from leagues away... at least, that's what they say.

Even more fun are the "highly theoretical and often rumored" special bolts that may or may not exist depending on who you ask. Skipper bolts can literally jump through space, effectively bypassing people, walls, entire armies... to hit the target from out of nowhere. Benders... bend around corners. Piercers generate a shaped edge to pierce through virtually anything.

Any special bolt like this, assuming they even exist, would be prohibitively expensive, and who's money could be arguable put to better uses. Though there's something ironic in being killed by a bolt that is literally worth more than you are.