[Lizardo]

A crossbow bolt is no more 'piercing' than an arrow. In fact the arrow typically has more mass and because of its length compared to cross section and fetching more flight stability.

The tip of the projectile is more important for the penetration of armor. The bows, and arrows, of Japanese Samurai were measurably superior to the English Longbow but the English arrows could penetrate both chain mail and plate armor. The Japanese arrow typically fails to penetrate chain (because Japanese knights never used it).

Composite re-curve short-bows are also very effective.

Penetration characteristics of a crossbow bolt are no different. It is simply easier to build crossbows and train crossbowmen.

Sling bullets just do not penetrate armor. They are blunt impact. You need gun powder to make a bullet effective. Slingers should though be able to carry 50 bullets and crossbow men 20 bolts.

Arquebus's were not so terribly inaccurate as to be useless, they killed or maimed what they hit and they reloaded as fast or faster than a crossbow with no strength needed. Breach loading versions were also available, just not widely so.

The use of crossbows and bows should be fatiguing, modified by strength.

What's also unsettling about shooting is the pattern of impact which tends to be all over the target area. Generally directed kinetic ammunition shouldn't stray too far to the left or right.

Missile weapons generally only penetrate at most 4". This means that shields should be very effective against most arrows/bolts and almost impossible for sling bullets.

An Arquebus will simply ignore shield and armor at effective range.

In this regard, distance should affect both accuracy and potential damage.

Bows could also be customized for the character's strength.