Thanx guys!
Juan Antonio, I have no idea what kinda elm this was; the only thing I know is that it was a small diameter sapling with no heartwood, harvested in Switzerland. I have not had problems heattreating this wood but I have witnessed chrysals on to strongly heattreated maple - probably overdried. Elm has big variance from sort to sort and tree to tree. Imho one should heattreat slow and deep. I either do it with my quartz radiator or with the heatgun always moving along the wood - never stop moving the heatgun. I typically move along the limb 4 to 5 minutes per session with the heatgun 1/2" away from the wood. stop when the back gets too hot to touch with your fingers. a too strong treatment can weaken and ruin the wood. using oil or solved resin helps for a better heattransfer and avoids charcoaling.
this particular bow received maybe 5 sessions of heat. I did induce reflex as well. In the beginning there was around 3 or 4" of reflex. The reflex got lost over time and many arrows shot. It also lost around 5# of drawweight since. It still has 1" reflex left now. It's still a very good bow and I hope its stable by now.
cheers