I heard an ominous cracking noise. The bow has fractured where there is a big S bend in the lower (left in the pics) limb. It's where there are a couple of knots, I'd been careful not to heat bend it at the knots and it's failed just beyond them where I did most of the straightening. The first two pics are with the bow strung to a high brace to open up the crack before I finally broke it.
It's been interesting working with the Hornbeam, but I obviously took on a bit too much with that stave. If you look back at the previous pics, there is no sign of a problem at that point
Once the crack appeared I took pics and finally took it to breaking point, it was still remarkably tough to actually snap. Overall I'm quite impressed with Hornbeam and will try again when I've got a straighter stave seasoned, I'm not too upset as it was always going to be a learning experience and it only cost me my time... well I managed to wreck my heat gun too (They are designed to be left standing nozzle up to cool down after use, but I left it on the floor in my haste to clamp up the bow during heat treatment).
Making bows is slowly curing me of my impatience and making me more philosophical about failure.