Artillery & Iron Daemon Train analysis
Hashut sent his blessing on you in this category.
Dreadquake Mortar - make advantage of its range 12-72. Always take Ogre to avoid slow loading and to add extra 4 wounds. Shoots S5 (S10 in center) with your small template and should be directed to enemy’s wizards, artillery, buff wagons, cavalry.
When taking Hellbound upgrade - be aware, as it bounds a daemon in your war machine and that means lore of light or Luminark may do a bu-bu to it. It is bit messed up, and to be honest you have to discuss it with your mates, but me and mine established eventually that Hellcannons and Hellbound Warmachines - as crunch keeps saying about bounding daemons in these - are daemonic. And that leads us to next paragraph - how to use your Mortar and artillery.
First of all - ignore the infantry with a rusty blade. Your infantry would and should deal with them. Dreadquake has task of destroying dangerous stuff, or to stop them from moving due to a Quake. So, unleash wrath of Dawi Zharr against Sorcerers, Warmachines, Monsters and This Empire General on a Gryphon. SNIPE. Turn your Daemonsmith to a sniper using a train-wagon-mortar.
In my last game I had 2 Mortars, Hellcannon and Deathshriek - not to mention blunderbusses, fireglaives, throwing knives and shooting Iron Daemon. Basically the only non shooty unit in my army was K’daai Destroyer. And boy - against Empire (tank, 3 cannons, 2 hellblasters, Luminark), Skaven (wheel, 2 zzzapguns, around 6 jezails, bell) and Chaos (2 Hellcannons, warshrine) I’ve been shooting all around like a maniac. At the end I’ve lost Deathshriek and one of Mortars survived Empire’s Luminark, and 2 shoots from cannon with 1 wound left.
Now, you have an idea now, how me and my mates do play our games - “No remorse, no respite, no regrets”.
Remember that as standard - all Artillery in the game is Move or Fire, so cannons hit by Dreadquake’s template have to pass the test if want to fire. As per description of Quake.
Daemonsmith nearby obligatory for re-rolls. Steam Carriage only as hard cover if you think you’ll be eventually within your foes shooting-non-artillery units. But Dreadquake on carriage looks soooooo damn good 
If towed by Iron Deamon, you may manoeuvre with your choo-choo-berserk-train to give a mobile hard cover to some of your infantry units.
And remember - as per FW FAQ - you have to use small template. If you have doubts - it shoots as Stone Thrower from Rulebook, and Stone Thrower uses small round template.
Deathshrieker Rocket Launcher - I never fired at characters with it. IT IS A WASTE OF A SHOT. Even with daemon-smith’s re-rolls it’s still too random - cos u have to get a direct hit. In terms of character on foot or a cannon it’s almost impossible. If you aim at something big or on flyer, or Chariot, or buff wagon it looks slightly better. But still - sniping shot is an act of desperation.
It is good however on delivering fire damage to flammable units (Hello Ashstorm my old friend…), or no AS infantry blocks. You use a large template, and roll, but if you missed the unit, you try to hit again with small template. So technically you roll to establish where, then you re-roll due to a daemon-smith’s re-rolls and if dices still hate you to guts, you roll 3rd time to get the hit into the target with small template now. Deathshriek is cheap comparing to Hellcannon or Dreadquake and much less reliable, so I took mine for LOLZ.
Once played 12 rounds - 4 armies - 23k-ish points game. Kept missing tragically through 11 rounds (1 hit), and then in 12th with a desperate sniping shot actually managed to deliver tactically critical hit and destroy Empire’s Great Cannon. Nice!
Hellcannon - Daemonsmith’s re-rolls make it more reliable then when set up in WoC army. Main thing to remember is that it is a Monster. Monster with Handlers, that shoots, and it is how it should be treated. Also as Monster it Thunderstomps when charged. Plus you have to do LD tests. Solid choice. But I’d go for a Dreadquake due to a range and Quake.
Magma Cannon - If you plan to sit around that hill and not to move for x rounds, DO take it. With Ashstorm it will leave ruin and smoking melting boneyard of your foes. 24" range? D3 wounds, proper S? Brutal. Just make sure you didn’t take too many, cos your friends may stop playing with you. Pity it has AS 3+
Iron Daemon - shooting - May move and shoot, may act even, when you’ll roll 2 x misfire, as you’d blow the cannons only.
The way it moves is slightly different than normal unit, yet similar to Empire’s Steamtank (btw: THAT THING IS BROKEN. I fragged it from 10W to 2W, and still couldn’t kill the thing. And it was still shooting. Awesome!!!)
It is a brutal and reliable machine, that grinds through infantry, and the only thing you have to be careful about are direct hits from cannons with S10. Short range of steam boiler cannons - 18 " only, but very reliable. Mine shoot to death Deathmaster Snitch, finished severely wounded Doomwheel, and stopped Skaven Bell and 40 clanrats. I can only regret I have only 1.
And don’t forget about Thunderstomp & Impact Hits
Iron Deamon - cracking
I didn’t use one - I wanted but FW removed it from its range. Simply speaking - Iron Daemon that does not shoot, but uses steam power to keep these drills running. Even more brutal when in combat with 2D6 Thunderstomps (compering to 1D6 of normal Iron Daemon), but has to get there.