Char cloth. The bore diameter is OK, but that small a bore x stroke means virtually zero clearance at full compression in order to get into the 20 - 30:1 compression ratio range. With a larger swept volume I would have considerably more headroom for a larger bit of char cloth. I was constrained on this one by the obscene way the "blank" split off from the log - by the time I got it turned, I was not comfortable going to a larger bore.

I read one person's report that osage orange fire pistons have a tendancy to "blow apart" after some use, but I am skeptical - maybe. Or maybe it was not fully seasoned and developed drying stresses -> cracks. We'll see - I'll make another, larger bore and longer stroke one next week as I have a little time. So far this one works well, but it takes practice.

Tom