Eh, the misunderstanding was my own fault.
Anyway it does make sense. Your mockup is about as elegant as this type of solution is going to get, other than lacking a method of keying it.
I’m not really 100% happy with any method I’ve seen or thought of for doing a series conversion on the M6. If there was a clean, reversible way to lock the body tube in place then I’d advocate Mike C’s method, but I just haven’t seen a good way to handle that either.
OP updated
Very nice, me neeeeds! lol
I have one in the wind at the moment to Australia in an effort to sort this out. Switching tubes to a modified TK75 extension tube so the carrier can be used. Hope it works! 
One (or two) of yours would be nice for the reversibility.
Subscribed.
Excited to see the results
Contact board is done. I made it from a full faced copper pcb from radio shack. It’s going into my second M6 to run 3 XHP-50s (soon to be 6) from four 25Rs using an old fubared M6 driver with just the FETs remaining. I hooked up the gates in parallel and I’m going to use the switch to run it momentary direct drive only. I’ll do my best to get some beamshots too tonight… but I’m not making any promises
That is one good looking creation JM. Very clever.
Nice work… can’t wait for the beam shot 
So now that I’ve got a day of use on the piece, with plenty unnecessary times opening and closing the light, I can say with confidence this is a reliable solution. The design is naturally keyed and at least in 2P2S, you can’t physically put it together the wrong way.
As you can see by the unused hole and leftover solder, I tried at first using a central spring for + plate to driver contact… this worked but added that much more effort to compress the springs and get thread engagement. Another side effect was the spring would sometimes bind the contact plate inside the head, where it would remain after you opened it up. Nothing terrible but didn’t prove to be an advantage over my second solution, which is better for current carrying anyway.
As for the beamshots, I’m charging up all my batteries today and am going to try and do a full shoot of my collection if the conditions are good. It was too foggy last night and everything is wet so not ideal conditions…
But I’m kind of mad I built this. Now my modded K40M and XML2 M6 look like they’re running on primaries, and any light that’ll outdo it will require a lot of $$$$$$$$. lol. Still cracks me up that we call it BLF
BLF is generally budget in the beginning for most of us, who then proceed to put $60 worth of parts into a $35 light.
Very cool and very simple solution. I like it. Do you think there is enough length for protected cells?
Yes. They should be no problem. EDIT I checked with four cells measuring ~69mm and I could only manage one thread before I gave up. With softer springs (I used some strong ones) and shorter/no positive contacts it could be done. I figure though if anybody is running this setup they are using IMRs anyway. End EDIT I only have two protected 18650s so I can’t prove it with pics but the way the unit works is there is no lockout. As long as there is one thread engaged I can operate the light. Of course this isn’t a recommended way of running something, I only intend to illustrate the concept at an extreme.
The O-ring on the body tube is still completely covered by the head when fully tightened, since added length is only 1.6mm. I’ll go do my best to simulate protected cells… might use some magnets or something.
You should be able to run it on one pair, two pairs is a bonus. Try the pair of protected cells you have and leave the other two out…
Regarding protected cells I’ll say I didn’t give them much/any thought during the design process. Like I mentioned in my edit of post #19, if the user intends to run protected cells, different hardware can be used to accommodate them. The body tube depth from front lip to face of rear pcb is ~70.6mm. This means with a std protected cell at ~69mm, you’ll have 1.6mm remaining for a spring. This is reasonable as long as the right springs are used.
NOW, for those that are really eager to run prot. cells AND have beefy springs that are resistance modded, you can always add some spacers under the rear pcb and gain tons of room (relatively). The body tube with this setup no longer carries current so any material can be used. I’ll measure but the factory screws probably are long enough to give you ~2mm comfortably.
Any updates?
Yes. I’ve revised the design to enable mechanical lockout with aprox a 1/4 turn. I’m still working on learning eagle. I’ll post 2D drawings of the design here tonight. I may ask for help from the community to get this drawn up in Eagle for the sake of time. I just don’t have enough time to devote to this at the moment. :~
8000+ lumens? 
Something around that It’s at least 2x my K40M that’s running full throttle…
Would you say its more of a flooder than a thrower now comparatively?
Just did a ceiling bounce test with these two head to head, both on fresh cells. Light meter on the floor, sensor up, underneath a wooden table the lights were tail-standing on. 14lux startup and 12@30sfor the M6, 5 for the K40M (steady). That puts it around 9k+ lumens startup.
Thrower is such a subjective term. My personal descriptions of a thrower may not match yours, but last I checked it did in the 70K lux range at 30s. I don’t remember startup values, or if I’ve ever recorded them.