A couple of years ago I purchased a fire piston, but I was never really satisfied with its performance.  So, I vowed to make myself one.  However, my initial attempts (using 1/4 inch copper tubing and 1/4 inch dowel, and 1/4 inch O-ring) were not entirely successful.  Although I get compression, it is not sufficient to ignite the charcloth.  It could be that when I sweet the cap on the tubing, there is a small leak or perhaps I need a better O-ring seal ... but I have one piston that uses 2 O-rings!

So, in my effort to make one of these, last night I ran across these videos for a home made fire piston.

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I whipped one together this afternoon, and it works like a charm!  It also has an advantage of making a nice large ember (as opposed to my 1/4" version).  BTW:  My compression tube is ~ 5 inches.

dd