Crossbow: short range, high power, medium speed, medium accuracy, medium ammo stacks
Gun: short range, very high power, slow speed, low accuracy, small ammo stacks
Bow: long range, medium power, medium-fast speed, medium-high accuracy, medium ammo stacks
Blow Gun: very short range, low power, fast speed, high accuracy, large ammo stacks
For more realistic, change it to following...
Crossbow:
medium range,
very high power,
slow speed,
high accuracy,
medium-large ammo stacksGun:
medium range,
medium power, slow speed, medium accuracy,
large ammo stacksBow: long range, medium power,
very-high speed, medium-high accuracy, medium ammo stacks
Blow Gun: very short range, low power, high speed, high accuracy, large ammo stacks
Reason:
Crossbow: In medieval context, crossbow is the most powerful weapon that can be used. A type of crossbow called arbalest is strong enough to pierce plate armor (its use against Christian and Catholics were banned by Pope Innocent II). Its draw back is the slow reload rate, beside that, crossbow IS overpowering in medieval warfare.
Gun: Gun sucks. In medieval time, the gun is overpowered by crossbow and out-ranged by the bow. It has one advantage, gun requires little training to achieve the same stopping power. In addition, a single user can carry much larger supply ammunition.
Bow: Medieval machinegun, a skilled English bowmen can fire at a rate of one shot per 4 second on average (not sustained, of course). Bow are also accurate at medium range but can reach much further then any other ranged weapon at that time while maintaining their killing power. A bow can also pierce some plate mails (won't pierce steel). However, bow requires a lot of training to use correctly.
Blow Gun: Actually pretty useless, but couple with poison can be deadly, and its low weight/small size allow the user to maintain stealth better. But during any shootout, blow gun user will get slaughtered at range.
Since the advantage of gun over bow during medieval time is purely the skill (or the lack of) required to use them effectively...
Skill/Attribute Effect:
Crossbow: Medium. High Skill will improve accuracy and reload rate. In addition, reload rate heavily depends on Strength. Sustained fire quickly exhaust user.
Gun: Low. High skill improves accuracy and reload rate (more improvement in reload rate, since early guns are so inaccurate that better skill won't improve the accuracy much). User don't get exhausted quickly from sustained fire.
Bow: High. High skill improves accuracy, reload rate, and power. Power and reload rate depends on Strength. Sustained fire quickly exhaust user.
Blow gun: High. High skill improves accuracy and reload rate. User don't get exhausted as quickly.