Why I will look twice before popping a another reflector in a C8

Bought a C8 for a friend. Tested it and it worked fine with the SMO reflector. Decided to see what it looks like with OP reflector(from same vendor). Unscrew the SMO and put the OP, and screw tight. Does not work. Hey what’s the problem. Remove the OP, and got a burning smell. :~ Put on the SMO back, this time lights only very low. That sucks. Change battery, same result.
Found that the spare reflector made a short because it is too large where it rests on the pill and fried something. Probably the driver.

Original C8 reflector (SMO)on the left, Spare reflector on right (OP)

Original reflector sitting on pill. It does not make a short, because base of reflector is smaller.

Spare reflector sitting on pill. You can see that it will try to sit flat on the pill when you screw the bezel…. and making a short. Bam.

On the left, the correct correct way to do things, on the right not so much. Only a thin piece of plastic is protecting the contacts from the metal reflector. When I saw the thin plastic the first time I thought, hey what’s that? Now I know, this is the cheap way to do things.

I have the opposite problem, my spare SMO is to short so glass isn’t correctly pressed by reflector and it bounces around. What’s more the LED sits too shallow, it results in poorer concentration with black hole in middle of beam. If I unscrew pill a bit (90-180°) everything is as it should be. It’s for Convoy C8

You are not alone in having this happen. There’s a learning curve for sure.
I put polyamide tape on the bottom of reflectors when there is a chance of the metal reflector shorting the positive and negative on a star. It’s ultra thin and a razor sharp blade is all you need to shave away the portion that blocks the emitter hole of the reflector.
If not polyamide tape, try fabricating an isolator of simple masking tape in a pinch.

That’s because that SMO reflector is not C8 reflector but Tiablo A9 reflector.

It's identical to the reflector that comes in a XR-E C8. XR-E reflectors have a wide flat base because the LED doesn't need any extra clearance to not short anything, the XM-L C8s have the narrow base reflectors as a lot of them use little 16mm MCPCBs. The XR-E reflector makes a tighter beam with the XM-L than the XM-L-specific reflector but needs a slight relief cut in the base, and attention paid to get the wire attachment solder nice and slim to maximize clearance. It also helps that to get the focus right they need a big thick spacer/centering ring of around .080".

Strange as that flat base reflector causing problem, I removed it from another C8 in fact, and both are from Kaidomain.
I orginally thought that it was a spare OP reflector that I bought but it was not. Now I remember that I swapped the SMO with the original OP one from a copper pill C8 and they have both same wide flat base.

I have never seen a XR-E C8 with the narrow base reflector, or a XM-L C8 with the wide base reflector. They can be swapped to get a nicer beam but requires some work.

Which LED came in the C8s your reflectors came from?

Led on copper pill is XML and the latest aluminium thin insulator one is XM-L U3
This spare C8 reflector SMO
In fact it is the 4th C8 I buy, the 2 first were flat base from Kaidomain and 3rd from Fasttech Convoy C8 narrow base. All XM-L led.

Ouchh, I learned this lesson one time in much the same way as you. Unfortunately mine heated the LED (poor XR-E) so hot that it re-flowed itself and spun about 45 degrees on the PCB causing it to look like it was off while it was actually a dead short, smoked the driver in direct-drive mode at this point, and ruined the 18650 powering the whole mess.

Actually I think that was my first “mod” attempt, way back when. Fortunately things have improved since then, and I never use a live cell to test a new modification, always current regulated bench power.