Crossbow Academy Pt 1: Crossbow parts and what they are for

Discovering a new hobby is fun but challenging. This first in Steambow’s Academy Series hopes to help you learn the basics. This time it's crossbow anatomy.

Are you new to crossbows but a bit confused by all the terms? Then this series is for you. Too often, people in a particular hobby, sport, or pursuit are so used to everyone around them knowing all the jargon involved that they forget everyone has to start somewhere, and often when they do, they won’t yet know the ABCs.

So this blog piece, and others in this series, will look at those ABCs and explain them in a straightforward way. In this piece, we look at the anatomy of a crossbow and why it’s there.

What makes a crossbow?

This is probably the first thing to settle. Everyone knows what a crossbow looks like, but what’s the technical (and often legal) difference between a crossbow and a bow? In simple terms, a crossbow does not need the user’s muscle power to keep it drawn and ready to shoot.

Whether just pulling the string back manually or using any number of cocking aids, once the string is cocked, the user’s physical input is no longer needed. With a vertical bow, when you stop straining, the bow just returns to a resting state.

There are, of course, other differences in appearance, but those are all a result of the vital difference above. Since you don’t need to hold it in the ready-to-fire position, the bow can be configured, aimed, and fired differently.

The bow part / limb

The one instantly recognizable bit is the part that looks like a bow. This “bow” is made of strong but flexible material. It can be made of one piece or two called the limb or limbs. Very often, limbs are simply fiberglass. Steambow’s AR-6 Stinger II crossbow series goes one further and uses a combination of fiberglass and carbon fiber. The string is fitted to the limbs and keeps them under a resting level of tension. When any bow is primed for release, that tension increases. It’s this stored energy that will later propel the arrow. The string normally loops over bits at the end of the limbs. These are called end caps or limb caps.

Types of release

If you’re not holding the string, then something else has to. Modern crossbows use a trigger and latch system to hold and release the string. Although the trigger might look outwardly like a rifle’s, internally it’s a very different story. The latch does not need to hold back a hammer or striker, but it does need to hold on to a string that is potentially under huge tension. This can mean some relatively complex engineering with its parts aligned just right.

In the case of Steambow’s AR-6 Stinger II range, the string retention is far simpler. It is a groove cut in the frame (which we will look at in the next section below). This does away with small internal parts prone to breakage or seizing, thanks to dirt. For that reason, Steambow’s choice of a frame-groove points to their drive for the highest levels of reliability you want in a tool rather than a toy.

In this instance, the trigger is very simple, consisting of one moving part (together with a return spring) compared to as many as, say, 10 in a latch release setup. The trigger has a block that simply pushes the string up until it clears the groove in the frame and returns to its resting position, powering the arrow forward as it does so.

Purpose of the frame

Consistency is the key to accuracy. In the case of crossbows (and apart from the users themselves), that consistency comes from the string being under the same tension every time and the arrow being propelled over the same distance before leaving the string behind and starting its unassisted flight.

Part of that is thanks to the frame or barrel. It first provides the rigidity needed to keep the string under tension: without it, what would house the latch and hold the string pulled back? It also provides the distance over which the arrow is propelled. The distance between where the string sits in the latch and the point along the frame where the string sits at rest is called the power stroke.

The power stroke is the only distance along which the string can transfer the stored energy of the limbs to the arrow. The amount of weight exerted on the string to make it reach the latch determines the “draw weight” of the crossbow. The presence of a frame also means that crossbows are capable of far higher draw weights than vertical bows.

Typically, if two crossbows have the same draw weight and shoot the same arrows, the one with a longer power stroke will have the faster arrow flight as it has had more distance to accelerate the arrow. Similarly, a crossbow with a weaker draw weight but a longer power stroke could achieve similar velocities to a more powerful crossbow with a shorter power stroke.

Other parts

The fact that the crossbow has that frame means you can also attach other things like a buttstock to rest it against your shoulder. You can mount accessories to the frame too. On larger frames, that might be a bipod for more stable shooting in a lying position possible. As with the AR-6 Stinger II Tactical or Compact, it could be a place to mount aiming aids, lights, or a quiver (although the Compact does not have a buttstock and is designed for shooting like a pistol). The AR-6 Stinger II Survival has a place to mount a scope for even more precise aiming.

Another part relevant to almost all crossbows (except the Tactical and Compact) is the stirrup: as with horse riding, the stirrup is for the foot. Any crossbow is cocked by pulling the string back. That motion needs resistance, and placing your foot in the stirrup on the ground offers that resistance in the form of your body weight and muscle tension.

So, in conclusion, on a crossbow the limbs are held in place by a frame that provides the resistance needed to allow you to cock the string and then leave it in that ready-to-fire position without further effort. That frame lets you also include buttstocks and accessories that can’t be mounted to a vertical bow, and the horizontal orientation of the limbs means you can more easily shoot a crossbow seated or prone, as well as standing.

Arrows are the last part of the basic equation, and you can read more about those in this blog about Steambow’s arrow evolution and this one about how to match them to your bow. Next time, we will look at how to load a crossbow safely.

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