LED drop ins and surefire shock absorbing heads

Owen said:

What is the drop-in?
There is some debate over the M2 bezel and heat with drop-ins, but I'll put that in a nutshell(or at least a couple of run-on sentences) for you.

-If you have a drop-in that does not utilize a spring between it and the body, then naturally it is in direct contact with the body, which is ideal for transferring heat from the module to the flashlight body and bezel.
In this case the M2 bezel's increased mass is probably better for handling heat than the standard bezel.

-If you have a P60L, or some other drop-in that does not make direct contact with the body, due to a spring, and therefore tranfers it's heat, however poorly, through the reflector to the front of the bezel, the M2's shock isolation will keep contact from being made between the reflector and bezel.
This means the heat won't transfer/escape away from the LED, so you might get away with the low mode on some multilevel lights, but if you run the LED for any length of time at anywhere near its spec'd current, you will overheat it(and kill it).

Battery runtime isn't the concern. If there is no route for the heat to escape, it will shorten, or quickly end, the life of your LED.

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Owen said:

YES. #4 is made to make direct contact with the body. 1 and 3 should also, as they're about the same size and shape when you remove the spring.

The below does NOT apply to the shock isolated bezel, only the standard bezel(but in case it helps familiarize you with using these dropins, I'm throwing it in at no extra charge). The shock isolated bezel will allow forward movement under pressure, so there will be no gap. Malkoff supplies a washer to ensure good contact with the SI bezel, and it is available for $1 on the website.

Using the standard bezel:
#4 will leave a slight gap on a Surefire, between the body and bezel, but not much. Whether 1 and 3 do or not will depend on how far in the module is screwed into the reflector. Sometimes unscrewing a it a little will slightly defocus the spot, making it larger, and help with the ring or dark spot around it-at the same time, that can make the total package a little longer, and cause a slight gap like with the Malkoff.
Don't be deterred by the word "gap". It's small, and the o-ring seal is well ahead of where the bezel's base butts up against the little rim on the body, so it won't compromise the light's integrity.

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Justin Case said:

If you look at the photos of your drop-ins, they all insert into the flashlight "neck" and stop when the flared part of the reflector contacts the top of the body tube. The wide, cylindrical part of the drop-in just below the flared reflector section provides the majority of the thermal contact between the drop-in and the flashlight body. Generally, that fit is not super-close -- you can easily detect a gap. The trick is to fill that gap with something thermally conductive -- aluminum foil, thermal compound, conductive copper tape, etc.

I don't think presence or absence of the outer spring matters since the tapered "pill" section doesn't have much thermal contact to the flashlight body anyway. With an outer spring, thermal contact is via the outer spring in contact with the pill and the flashlight neck. Without the outer spring, contact is mainly just at the outer edge of the pill/driver where it contacts the typical ledge at the bottom of the flashlight neck (you can see this with the usual DX drop-in from the mechanical scratch marks left in the solder blobs that typically ground the driver to the pill).

With a standard SureFire 6P bezel (the Z44), the top face of the drop-in also makes thermal contact with a metal shelf in the Z44. This can provide some additional heat sinking capability, especially if you haven't filled the gap between the drop-in body and the flashlight neck, as described earlier.

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