Thanks for the links.Since you're not using it for data, you might also try CAT3.
It's still 24AWG, but if you've used phone wire in the past, I think most of that is 24 as well....
Sprinkler wire is on ebay too...
Or Amazon.. https://www.amazon.com/dp/B00004S1UZ/?tag=skimlinks_replacement-20
That's 7 conductor 18AWG. It will handle current much better than the 24AWG phone wire will.
http://www.nar.org/safety-information/model-rocket-safety-code/Launch Safety. I will use a countdown before launch, and will ensure that everyone is paying attention and is a safe distance of at least 15 feet away when I launch rockets with D motors or smaller, and 30 feet when I launch larger rockets. If I am uncertain about the safety or stability of an untested rocket, I will check the stability before flight and will fly it only after warning spectators and clearing them away to a safe distance. When conducting a simultaneous launch of more than ten rockets I will observe a safe distance of 1.5 times the maximum expected altitude of any launched rocket.
If there's steel strands it could be used for igniters, steel bridge works for most club launchers.The reviews say it's stranded, mostly copper with a couple steel strands. It wouldn't be my first choice due to the gauge, but it's not terrible. If you have a home improvement store around, or an electrical supply, there are better options.