Mark, I'm really excited to see that you went ahead and did it!!! Great job! I'll add it to the charts as soon as possible....
I'm not aware of a definitive way of getting 3 17500s into an M4... but with a 1 cell extender it might be doable, maybe with a spacer or spring stretch.... unless someone is making 1/2 cell extenders I am not aware of?
The 3x17670 will work with 2x 1 cell extenders on an M4, or 3x 1 cell extenders on an M3T.
To use 18mm cells, boring the M3t or M4 (and extenders) or buying leefbodies will be necessary.
IMO, the best places for these lamps will be in M6s with 6xRCR123s and 3x18650 leefbodies with M heads.
For those who just want the all important answer "how bright." I'll try to break it down to the best of my ability... use these numbers to compare within this comparison only. So if you own one of these flashlights, you can assign this "value" to what you have, to get a better idea of what you get when you switch to a lithium-ion setup with a LF lamp...
An M6 with HOLA on lithium primary cells, Will ramp from around 650 torch lumens down to around 550 torch lumens, in about 15-25 minutes. (depending on cell quality)
An M6 with LOLA on lithium primary cells, will ramp from around 350 torch lumens, down to around 275 torch lumens, in about 50-70 minutes. (depending on cell quality)
An M4 with HOLA on lithium primary cells, will ramp from around 425 torch lumens, down to around 350 torch lumens, in about 15-25 minutes. (depending on cell quality)
An M4 with LOLA on lithium primary cells, will ramp from around 275 torch lumens, down to around 225 torch lumens, in about 40-60 minutes (depending on cell quality)
Now... for comparison with the above statements, I Figure the following.
An M6 loaded with RCR123s and a HO-M6R, will ramp from around 500 torch lumens down to around 300 lumens before you should recharge. Runtime will be anywhere from 25 minutes to 35 minutes depending on the cell quality.
An "M4" style setup with 3x17500s, 3x18500, 3x17670, or 3x18650, will all have a pretty similar ballpark behavior as far as beginning and ending brightness with an HO-M6R. the difference is actually more noteworthy from brand to brand than from size to size... Pila cells seem to really hold the highest voltage under a load, and will deliver the best performance.. larger sizes will of course deliver more runtime, with 17500s delivering about 30 minutes, and 18650s delivering about 60 minutes. Brightness will ramp from around 550 torch lumens down to around 350 torch lumens over the course of the run.
In conclusion, the HO-M6R is positioned very appropriately. I can say with confidence that the 2.1A draw is IDEAL for maximum power while maintaining safe operation in an M6 loaded with RCR123s. It's a perfect balance point. Most cells on the market right now are delivering about 500-550mAH at ~1A (will be 1.05A per cell in this configuration)... so we're right at ~2C on this lamp, which is safe for continuous operation. This was really an ideal and respectable design decision. Mark, you ROCK!
