The Situation
So, my family has some history in archery. I'm not a particularly great shot, but I'm competent to hit a target consistently at short ranges. I recently got back into archery, and was thinking about it in Mythras terms. Since I'm starting again, I decided to go with a compound bow. While I've shot them before, it's been literal decades, and tech changes. This time, I'm embracing the tech a bit. We're going to discuss modern archery a bit here, and how to implement it in Mythras.
Why not guns? Why use bows?
This is a pretty valid argument. Guns have a lot of advantages over bows. Longer range, higher rate of fire, more lethal per round, easier to train, you can even go prone and shoot (however, see crossbows).
Bows have one thing that guns don't - stealth. So called silencers don't really silence them, no matter what Hollywood says. They do a fine job of protecting your ears from the worst of it, but it's still pretty clear you've fired any normal round of ammunition. Subsonic rounds exist, of course, and these help, but there is still quite a bit of room for improvement. A bow is nearly silent.
How does this translate to Mythras?
The first thing I would say is that guns are easily identifiable by location at an extremely long range. Essentially, no perception roll necessary for most ranges to know there is a shot happening, and it is Very Easy to identify where it is coming from roughly. The bullet leaves the gun at multiple times the speed of sound. For example 5.56 leaves the barrel at about 3x the speed of sound. While it does slow down, consider that once the bullet is 1 second out, it's well ahead of the sound wave.
Bows, on the other hand, require a perception check to determine a shot has been fired by sound alone. It doesn't move faster than sound, so it becomes important to be as undetectable as possible.
The Rules
Firearms are audible and locatable at anywhere inside their close and effective ranges - no perception roll to determine approximate location. That doesn't mean you can locate the shooter, just that you have a pretty good idea where he is. At Long range, it gets harder, as the sound has become indistinct, but still not horribly hard. Call it a Very Easy roll.
Bows, on the other hand, are extremely stealthy. Anywhere in effective range, the perception roll is Formidable, and Herculean at Long range. At close range, it is Hard.
The Compound Bow
Mythras has short bows (which isn't really a designation, but lets ignore that), longbows (and as the authors are of UK descent, one can presume they mean staves of yew and all that), and recurve bows, which I can presume are the bows of horse archers, and generally composite varieties.
Compounds operate very differently. They have a pair of wheel-like things called cams (though they aren't really cams) on the ends that act similar to pulleys. Since they are asymmetrical, they provide something called "let-off". Because of this, they experience their full power early in the draw, and holding it back by your cheek ("at anchor") is MUCH easier. Mine, which is very cheap and off of Amazon, has a 65% let off, but others have north of 85%. Regular bows do not have this. They, in fact, have the opposite. They get HARDER to hold as you pull back farther.
Modern compound bows also have a bewildering number of attachments you can put on them. Modern bows do too, but compounds are something special. Sights, levels, trigger releases, arrow rests, string dampeners, wheels for adjusting your draw length, stabilizers, on-bow quivers, and many more. Truly anything to get you to buy more. Perhaps this reflects on modern archers being numbers nerds.
The thing about all of these accessories is that none of them really are designed for rate of fire. They are designed for marksmanship, hitting the target consistently every time, not alerting your target (thank you bowhunters), and being able to operate in the brush. Joerg Sprave is about the only person to have come up with an attachment to make bows shoot faster, which is called the Instant Legolas.
Modern arrow technology also moves a different way. Medieval longbows have big, fat arrows that weight something like 800-1500 grains for an English longbow. They hit pretty hard, but they also move pretty slow - around 180 fps. Modern compound bows are more like 500 grains, quite a bit thinner, and shoot up to 310 fps. This makes them behave much differently - flatter trajectories, different physics. I'm not going to enter that fray other than to say that modern compound bows often show higher kinetic energy, and this translates to penetration.
Modern arrows also have multiple head possibilities, but the most common are field points and broadheads. Field points are narrow, small points with no edges. Broadheads are much wider, essentially having razor blades off of each side.
There are a lot of factors here, and we aren't doing GURPS here :)
The Rules
Start with Recurve Bow stats. Consider allowing the Overpenetrate special effect.
For simulating the power - Shift up the damage modifier of the shooter by 2 steps. This makes a nice emulation for those of us who are not Joe Gibbs but are able to loose arrows at the speed he's putting down range. Allow the Overpenetration effect.
An alternative would be to give the arrows Armor Piercing equal to half of their maximum weapon damage. This has the benefit of not escalating the damage, but the downside of not providing much mechanical assistance to those with low or negative damage modifiers.
For simulating let off - This is a pretty fine detail, but I would lower the fatigue for combat with a compound bow down to a Light activity, similar to walking.
For simulating a sight - You can reference a telescoping sight (from the firearms supplement) for this. Extend the Close Range of the target by the multiplier of the sight (normally only x2 to x4). Do not reduce the apparent distance to the target, as this is a function of magnification.
For simulating stabilizers, levels, and so on - I think it's best to just package these as a unit and give the archer an additional grade reduction when Aiming.
For on bow quivers - reduce the reload time by 1 until the quiver is empty (usually 4-6 arrows, with 5 being extremely common).
For Broadheads - These have the Bleed trait as well as the Impale trait, as they are designed to cut through flesh and blood vessels. Some may additionally have the Barbed trait, making them very difficult to remove.
There are many other options out there for modern archers. Destined has a whole section on trick weapons.