SpudFiles

Is sparks plugs (the same used on combustion engines) better than using screws to ignite propane or MAPP, and what should I use with the spark plugs, a stun gun?
And is it possible to use various spark plugs wired in series ?

I'm going to make a new combustion cannon, but I'm thinking in make it with steel or aluminium, so is there some risk that I can be electrified by the ignition system ?

Nope, there is no difference between spark plugs and anything else. So long as they make a spark travel through the air it's fine.

Yes, there is a risk, but only if you complete the circuit as the path of least resistance. I think you'll find that the sparks will short to the chamber, and if you are touching the chamber and an electrode, it'll go through you.

Basically, if the total length of air between the electrodes and you is less than between the spark gap electrode, you'll get shocked.

I think you need to do a little research into how electricity works, just so you understand the concept.