Originally Posted by kernelkrink
A possible problem I see with using Vaseline or other "fuel" is this is essentially just a small diesel engine, if the fuel ignites like it does in a full size diesel the pressure produced could be substantial. The piston could be ejected with great force.
I agree, there was an article in either the American Rifleman or Guns magazine many years ago that showed bb guns that used the compressed air type piston that had exploded from using petroleum based lubricants. Vaseline was one of the lubricants mentioned as I recall. While the fire piston will probably not match the compression of the piston in an air rifle, I would be very careful and procede with great caution. From what I have read 'chaga" which is a type of fungus that grows on trees in the north east is the best combustable to use as it will produce an amber that will burn for a long time.