Artillery is mostly for use against castle walls rather than people. While most artillery can shoot at people few can actually hit them. For the most part artillery is useless unless you need to attack a fortification, when you are up against some of the advanced castles you will be glad you packed a trebuchet or two! All gunpowder or stone missile flinging weapons fire missiles that can bounce on impact. The ballista is the only weapon that does not have a bouncing missile.
Ballista
Ballistae are the worst artillery hands down. They do little damage against
walls and have a short range (for artillery, compared to archers it is a long
range) and this often leads to their crews getting killed by castle defences
before they do much damage. Against people ballistae are reasonably accurate but
since the missile will hit one, and only one, man they are not as good as the
more conventional missile units. Ballistae can turn in place.
Bombard
Bombards are primitive gunpowder weapons available to the Christian factions.
They are slow to reload but they have good range and damage. They cannot turn to
aim at other targets so you must position them exactly where you want them in
the battles deployment phase. Bombards tend to explode, however they do have a
certain number of guaranteed safe shots (I think it is 4) before they are at
risk of blowing up.
Catapult
Catapults are the first decent siege equipment you get. They have enough range
to bombard the more basic castles without taking return fire, however the mid
level and advanced castles will have the range advantage. Catapults can turn in
place so set them up in range of several juicy targets and let them work their
way along them. The catapults stone missile will bounce on impact; the number of
bounces is dependant on the terrain, angle of the missile etc just as in real
life. This makes them reasonable against tightly packed infantry. Aim at a set
of units very close together and target the foremost unit. The catapult will
probably miss but the missile may bounce right through the other enemy units.
Higher valour really helps accuracy – at valour 0 they will probably only hit
their target one in every five shots.
Culverin
Culverins are proper cannon with a huge range. They can turn in place to attack
new targets. The reload time is quite good for a siege weapon and accuracy is
also quite good at low valour. The missiles do loads of damage to walls.
Culverins can be used against infantry with some success but they are not
exactly best used like that. If you need to demolish a castle as the Christians
the culverin is the weapon of choice in the gunpowder age.
Demi cannon
Demi cannons are massive contraptions that are set up and not moved until the
siege is over. They have good range and firepower so they are quite useful to
the Muslim factions. They have a very slow reload time.
Demi culverin
Demi culverins are smaller versions of the culverin. They have less range, less
firepower and the same reload time. They will perform with some effectiveness
against infantry if they are in a good position and firing into a mob. They are
quite handy but always take proper culverins over demi-culverins when you can.
Mangonel
Mangonels are the best pre gunpowder siege weapons. They have good range and
power but a very slow reload time. They are horribly inaccurate at valour 0 –
I have seen a mangonel manage to miss a large castle wall with all but three
shots until it ran out of ammo, considering that they have something like 28
rounds that is a lot of misses! Mangonels cannot turn once set up. Mangonels are
not anti-personnel weapons so use them against castles or not at all.
Mortar
Mortars are gunpowder weapons for the Muslim factions. They have quick reload
times and a wide trajectory of fire. They cannot turn after being set up though.
They are reasonably powerful but there are other, better weapons for bombarding
walls. Not very good against people at all.
Serpentine
Serpentines are true anti-personnel weapons. They are not very good against
fortifications but they are the best siege weapon to use against people. They
are very fast to reload and have a long range. Their power is very lacking
against buildings but the missiles still kill people in one shot. They can turn
after being set up and when they have a few points of valour they are quite
accurate as long as their target is not moving. If you absolutely must use
artillery against people this is your tool.
Siege cannon
Siege cannon are the longest ranged artillery in the game and exclusive to the
Muslim factions. They are obscenely powerful and can demolish a wall in just a
couple of shots. They cannot turn after deployment, and the reload time is quite
long.
Trebuchet
Trebuchet are a slightly weaker version of the mangonel. Read that section and
substitute average power instead of good power.