If you have the equipment and the skill go for it. It’s an excellent solution. :+1:
And unless someone beats me to this response this will be post number 4000 in this thread! 
If you started with an enlarged ID, then smaller diameter batteries could always be compensated for by inserting rolled up layer(s) of paper shims.
I wanted to try out the impressive looking Shockli 26650 5500mah until I found out it was 26.7 mm +/- 0.2mm.
Actually I’m not one for sloppy battery tubes and at 26.87mm Regular batteries are sloppy! You want to use oversize batteries, look at it as a chance to custom fit the tube, which I love doing!
Really all you need is a High Speed Variable drill and 1/4” rod from Home Depot or what ever, sand paper, a hack saw.
Make a Flapper!! 
I like a custom smooth fit to my weapon lights and even after single point boring I flap out the bore to fit, adds a bit of drag to the cells, helps with recoil, slows the cell (s) from slamming into the driver, that and limiting travel of the cells using rubber bumper (s) at the driver end or both ends, depending on the tube length and cells. Even my Combat lights/flashlights, ever drop a light on the bezel end and have the cells crush or bottom out the driver spring, called coil bind, I have…… once! 
Is there anything wrong with Orbtronic 26650s other than the price? I don’t know what they are under the wrapper but their protected and unprotected cells fit my L6 (black) just fine. Their 18650s seemed to test pretty well.
Thanks KawiBoy1428, I’ve improvised tooling quite a bit in the past. I’ll have check to see if I can even find my cylinder hone, it got retired after my muscle car era. It may be to fine of grit for removing material plus grinding stones tend to easily load up with aluminum, in which case they just burnish and generate heat. I also have a few sizes of drum sanders, as well, in different grits.
Same problem. Got my L6 a couple of weeks ago and yesterday got 2 of the recommended keeppower protected. I think I could force them in but would never get them back out. I have inquires in at keeppower and my supplier. I am hoping the just double wrapped this batch. I can’t imagine we all have to get our lights bored to fit new batteries.
Acquire liitokalas without protection, I have added resistance handle about 7 amps in the tail, there is no risk, a few days ago I produced short circuit in two of these batteries nothing happens at all.
…until you next charge them. 
Hi, I’m sorry, I do not speak English, I use a translator, I clarify the short circuit, it was not in the flashlight, I was measuring charge and opsssss, I made a mistake with the multimeter, the batteries died, but no exploits or anything like that, greetings.
I saw your follow up to this post. This message taken at face value as it was written is bad and dangerous advice that I do not want anyone to follow. I mean no offense to you and I thank you for clarifying that you do not speak English and are using a translator. We have people from all over the world here and all are welcome. Some things do not translate well. Short circuits in lithium cells are always to be avoided as the results can be very bad. This fact is the very reason that Simon clearly said that he only recommends high quality protected cells for use in the L6. Experienced people can do what they wish and many here do so and quite safely but this takes research and knowledge of the battery chemistry and much more. There is a very good thread covering all the basics of lithium ion safety here.
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1st attempt to hone out tube using a brake cylinder hone worked out ok. As I suspected, the stones are not that aggressive. Enlarged 0.06mm, the first .03mm went fairly quick until the hone loaded up with aluminum. The spring loaded three arms maintain an even pressure, and keeps interior nice and round. After honing with the stones, I wrapped them with gray scotchbrite then a cloth with compound for final polish. Next time I probably start with wrapping with coarser grit sandpaper or emory cloth.
Any likelihood of there being a diffuser produced for the L6?
I second the request for an L6 diffuser. L2 diffuser would be awesome as well.
The only problem now, ETex, is that the inside of the tube has no anodization and if you get a nick in the wrapping of a cell that can touch the inside of the tube the light will come on regardless of the switch position. So be sure to keep a check on your cell wraps to maintain integrity.
Dale,
That’s why I had previously asked if it would be a bad idea. Especially with protected batteries and the metal positive strip running up the side of batteries. Then I checked continuity from the inside tube walls to the edge at tailcap & found spotty areas where I had continuity.
I wouldn’t use protected cells in it, for that reason. The worst that could happen with un-protected cells is that the light comes on. With protected cells it could direct short one or both of the cells.
The spotty continuity is probably due to some areas having thicker anodization than others or some of the tube was not concentric so only the high spots ground off for a uniform tube diameter and left those areas without ano.
It’s not a Huge deal, just something to be aware of. (unless of course you’re using protected cells and then it COULD be a Huge deal!)
At the end of the day it’s no real difference from the battery tubes I make for my scratch built lights. None of those have any ano at all. (I also never use protected cells)
Richard sells a Kapton tape (or used to) in a 2” width, this would be ideal to put a layer around the cell to act as a very thin wrap and give some tube separation. The Kapton tape is really very very thin but strong. Worth checking into maybe.
I should have said more the continuity test was “before” I honed the tube.
Interesting. Any sign that they may have machined the inside of the tube after the ano was done? To true it or to fine tune inside diameter? (anodization can cause dimensional growth that can sometimes be unacceptable.)
Not sure of that. I only check a few spots on inside with my meter, and questionable area were very small and random.
Probably why the Protected batteries are getting bigger, thicker casing’s or double/triple wrapping, to lessen the chance of the fitz fitz… BooOOM!