My almost totally unsubstantiated understanding is that you tend to get less graphite and more binders in mechanical pencil and leadholder leads, because they need greater mechanical strength to stay in one piece without the support of a wooden matrix.
I can say that lead extracted from a Dixon Ticonderoga produced considerably less smoke than an 0.9mm Pentel-branded mechanical pencil lead when I drove five amps at 30VDC through both of them in turn, as a test of whether a newly arrived bench supply, cheaply bought from a no-name manufacturer, would live up to its rating. Both leads eventually glowed cherry red, as would be expected of any small-diameter carbon resistor dissipating 150W, but I wasn't equipped to measure such temperatures any more accurately than by eyeballing the emission color, which suggests a temperature in the rough neighborhood of 800-1000°F. On the way there, both leads cooked off everything that wasn't carbon, the Ticonderoga lead producing a faint ribbon of smoke that ceased after a few seconds, while the mechanical lead, despite its smaller diameter, released such a robust and prolonged emission that I wondered whether it might burst into flame. Once they'd cooled back to ambient, I handled both leads, and found the Ticonderoga about as sturdy as it had initially been, while the mechanical lead became extremely fragile with the loss of whatever waxes had burned off; I wasn't even able to remove it from the test jig without breaking it several times, and when I carefully loaded the largest piece into a pencil and tried to feed it for a writing test, it was too weak even to stand up to the clutch.
I haven't tried it with leadholder leads, not having enough use for such tools to own any, but I'd expect a result closer to the mechanical lead than the wood-pencil one.
I can say that lead extracted from a Dixon Ticonderoga produced considerably less smoke than an 0.9mm Pentel-branded mechanical pencil lead when I drove five amps at 30VDC through both of them in turn, as a test of whether a newly arrived bench supply, cheaply bought from a no-name manufacturer, would live up to its rating. Both leads eventually glowed cherry red, as would be expected of any small-diameter carbon resistor dissipating 150W, but I wasn't equipped to measure such temperatures any more accurately than by eyeballing the emission color, which suggests a temperature in the rough neighborhood of 800-1000°F. On the way there, both leads cooked off everything that wasn't carbon, the Ticonderoga lead producing a faint ribbon of smoke that ceased after a few seconds, while the mechanical lead, despite its smaller diameter, released such a robust and prolonged emission that I wondered whether it might burst into flame. Once they'd cooled back to ambient, I handled both leads, and found the Ticonderoga about as sturdy as it had initially been, while the mechanical lead became extremely fragile with the loss of whatever waxes had burned off; I wasn't even able to remove it from the test jig without breaking it several times, and when I carefully loaded the largest piece into a pencil and tried to feed it for a writing test, it was too weak even to stand up to the clutch.
I haven't tried it with leadholder leads, not having enough use for such tools to own any, but I'd expect a result closer to the mechanical lead than the wood-pencil one.