I find the real challenge is when you have had too many caps so you lose focus when heating it. Of course you end up with a "feel" for the heating cycle & I often find the unit clicking several seconds after I remove the flame if I lose track. Never fails to scare the shit out of me when .2 of a second before inhaling it clicks in my face
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Yeah, the caps get tired if you abuse/overheat them a lot too. My OG cap that I abused a bit is just not nearly the same as when I unboxed it, George offered to replace it, but I've been trying to get in 'mind over matter' mode with it. My mind is the click, etc. The old OG cap (original design, i guess OOG cap) started with 2 clicks that were "about a second" apart with a single flame. Over time, as its click got later, the two clicks got closer and closer together. Then, it had only one click, then that one click failed. Then I squeezed it in a way that somehow brought it back to life for like 50+ loads at this point. My theory was that the tip had been smushed just a little from going in and out of the tube so much, a few drops, putting the cap back over the glass too hard etc. Anyway it now usually clicks twice, close together, and I never get 3 cycles from a load, always 2 or sometimes even 1 (not going more than .5s past the click).
My newer cap for the Ti came out of the box, and remains with two clicks very close together, like an "8th of a second". Often on cooldown it clicks only once, sometimes on heatup it clicks only once.
Because I have draftiness/smell issues in my building, I generally can only take one hit. So I always heat past the click on my newer cap, up to 4 seconds. There is very little left in the next cycle, sometimes there is a tiny bit of green, sometimes not, mixed with dark brown, and occasionally, but not often, a little black/charry taste. Not full on combustion though. The old one, even the click sometimes is too late if you heat too far from the tip, you can combust, full on see and taste the cherry of awfulness.
So, it appears these can get "tired" with extended/hard use, I should note I did usually heat that original cap past the click, like I do my new one, this could also accelerate wear. I'm not really sure if physical roughness or # of cycles or high heat is what causes them to "get tired", but the fact that I was able to "massage" my caps clicker back to life may be a clue.