Something I Might Be Able To Make-Dwarven Engineering Schematics Here!

Well... we have water pressure now, so this got me thinking. I guess this is a part suggestion for allowing sufficient liquid pressure to displace blocks, but... here's my idea.

Me and my friend explore a cave. As he chips away at a wall, he uncovers a new room. I shine my light through the gap and tentacles grab me. "HOLYWHATISTHATAAARGH" I say, rather politely to my buddy, who had not yet noticed my perdicament. After he calmly finishes his ore vein, he cuts me loose. Swords won't work on this beast... we knew what to do though. I dig up, he digs down. I find a lake and drain it through a channel into a hastily constructed tank on one side of an unfortunately phallic-looking structure. He pressurizes some magma for the other tank. I set the water loose and it trickles over the front of the barrel. He releases the pressurised magma into the barrel. Blocks of obsidian spray the wall of the other room. This, my friends...
Is the Dwarven Railgun.
I suppose pressurised oil and a torch would make a Dwarven Flamethrower, and acid wouldn't need any pilot light at all, so we have the Five In One Dwarven Death-Machine!

It shoots water! Acid! Fire! Magma! And also an obsidian machinegun for those tricky corners! Please post comments and ideas. NO TL;DR FOR YOU.
Also is the Obsidian Gun even possible?

 

Mind=Blown
That whould be bloody epic.

 

I like this idea a lot! This would be an awesome and interesting way to kill enemies. Although I'm not sure if it would be entirely possible (I really hope it is ^.^)

 

Pressurised liquids? Water, acid and lava will DEFINITELY work, get a pilot light and the flamethrower will...the water over the barrel makes obsidian (Terraria logic) and the lava pressure builds up... FWOOMPH!

EDIT: Which is where the block displacement comes in.

 

I'm not too fond of lava+water=insta[insert some sort of stone/glass/whatever lava hardens into], but it seems water pressure makes a good railgun nevertheless

 

In most games, obsidian. In real life, cooled with water? Probably granite, if the whole thing didn't explode.