I currently have a couple of older Uniquefire UF2100s that I really love and was wondering if there is currently anything smaller out that’s using the XM-L2. I’d prefer if it was as bright as the UF2100, hopefully even brighter, and definitely no bigger. And not the DQG. I’ve read some not so good things about those.
Convoy S3 or Convoy S6 with an XM-L2, XP-G2, or triple XP-G2! They aren't much smaller but it's hard to get any shorter with an 18650 and keep a clicky tailswitch. There are some nice 16340/14500 lights out there if you can deal with the shorter runtime. I'm sure that others will have some other ideas, these are just some that I have experience with.
Illumination Supply offers them pre-built with an XM-L2.
XP-11
The UI can be cycled in less 2 seconds to power off. I love mine.
For only 12 bucks you can’t beat it!
This meets your budget criteria.There are other 18650’s that are smaller.
Get the Convoy S6 from Richard, clean, simple, nicely built and about all the light you can get with one 18650 and not be much bigger than the cell itself.
You put the driver and emitter in and the host is less than $11 bucks. If you don’t have the driver and emitter, he’s got those as well for $4.20 and around $6. If you can’t assemble the parts, he can do that as well and will also bump the stock output if you so desire. Really, the best way to do it and the best place to get it done. Even has a nice selection of cells to power it at very reasonable prices.
One Stop Shopping for Flashaholics. 
My suggestion will take longer.
The XP-11 offers a clip, side switch & magnetic tail cap.
Buy both of them!
Go with RMM's light for maximum lumens per unit of volume.
It sounds like you want small, bright and XM-L2.
You can get a lot smaller than any of the lights previously mentioned if you switch to a smaller battery type. You can get or mod a 1x16340 or 1x14500 light that’s half the previous suggestions.
Note that on a smaller cell you won’t get much runtime on high. But if all you want is a pocket rocket, perhaps runtime on high isn’t vital.
Is there actually a 16340 or 14500 that can put out 5.6A that RMM's lights need? It seems like most of those small cells top out around 3A. 1000 lumens can be achieved though.
Nope. The small cells can’t put out that kind of current.
Ah I just noticed the thread title specifically mentioned 18650. Didn’t see that in the body of the first post.
RMM’s Convoy S6 modded with 5.6 amps and triple XPG2 would be a good choice.
I seem to mistaken. It's 5.8A. He must use the original either 350mA 7135's and add either 380mA 7135's. It'd be 5.6A if all 7135's were 350mA chips, and 6.08A if they were all 380mA. What's twisted is now I was that extra 0.2A. It's a sickness.
AW IMR cells will do it, with an 18350 I’ve seen over 7A on a triple XP-G2 in direct drive. Now running it at over 5A with a Qlite. This is in an Solarforce L2m shorty, making some 1500 lumens otf. I do, however, have 3 ounces of copper in the head of this light. Makes for a surprisingly solid feeling compact light with a whole lot of output! Not a thrower of course.
Get them both. You know you want to. You know you will. Resistance is futile.
The brass flashlight from CNqualitygoods seems to be very small. However the XM-L2 version seems only be expected to be able to run on high for 5-10 minutes before it becomes too hot. Needs unprotected batteries. Just 97mm x 21mm! The UF-2100 is 120mm x 23 mm. The 18650 DQG is 87mm x 25mm(head diameter) x 22mm(tube diameter).
(Click image…)
I have one in transit, but it is the XP-G2 R5 version.
What’s RMM?
RMM is a member here. His site: http://mtnelectronics.com/opencart/
See the first reply.
roche f12
Nuh-UH! Resistance is QUANTILE!
Sorry, if you don’t like my puns, at least follow the link. The point is, around here, the answer to ANY question has to include the possibility: “The One You Make Yourself Is!”
(And I’d like to bump the idea of using a thin disc of QTC film to vary brightness, since the XM-L’s performance envelope pretty-much matches the 18650…)