EDIT: Did not realize I had an E2ST head in the intial review... E2HT review is later in thread. Corrections made to reflect the propper weaponlights.
I had an Arisaka 300 series on an ultralight build. It is a great light, but only 300 lumens on a 123 cell and limited range. I considered a Modlite 18350 light for the extra power, but it is significantly larger and heavier, not to mention more expensive.
I also had an Arisaka 600 series version with Malkoff E2ST head that uses a 16650 battery on a duty rifle that was swapping out to a Modlite 18350, so I had a spare Malkoff 600 series head needing to be used on a long gun.
My thought was, I could use a similar 3.7v short cell (like how the Modlite uses an 18350 vs 18650) and only suffer less runtime and no 123 cell compatibility (just like Modlite).
There was a problem with that though... the short 123 sized lithium ion cell is the 16340 cell. Traditional lithium ion chemistry really does not work well in that tiny size. Not only is the capacity limited to 500-700 mah, it also has a draw limit of 2A or 3A before the protection circuit cuts it off for safety, and the higher the draw, the lower the capacity, sometimes not running at over 2A due to protection circuit, sometimes only 400 mah capacity due to lower capacity near max current limits.
The traditional lithium ion chemistry inherantly requires a protection circuit to be "safe" either in the cell or light. The combination of the reduced room in a tiny cell 16340 cell from the protection circuit and the low draw due to cell size, results in the problems that makes traditional 16340 cells a poor solution for high current draw lights. The Malkoff 600 series heads are high draw, so I could not get more than 0-10 minutes out of a traditional 16340 protected cell. This simply would not do.
Then I discovered a new cell chemistry type recently released for the 16340 cell size. The battery is a 7A draw rated INR cell. INR is common in larger cell types, but unneeded for larger cells used in most flashlights. But these new 16340 INR cells have a capacity of 800 mah and dont suffer lower run times from high draw applications. The INR (Lithium Nickle Manganese Cobalt) cells are inherently safer, not requiring a protection circuit, and that combines to making it the best 16340 chemistry for tiny high draw lights.
The best battery out now for 16340 is the Vapcell 16340 INR 800 mah. These things are also cheap. Only $3.99 from 18650batterystore.com so I bought 4 to experiment with. The cells are light, only 18g vs 26g for my 18350 Keeppower protected 1200 mah. Comparing my Modlite PLH and OKW heads they are twice the weight of the Malkoff E2HT/E2ST head, 64g vs 32g. The Modlite body is a tiny bit heavier, but the tailcaps for both are almost the same weight at 13g for Arisaka and 14g for Modlite. The total weight difference, with battery installed, for complete lights minus mount is about 1.5 to 1.6 oz lighter for Arisaka vs Modlight. For an ultright build this is significant.
For output, the OKW at 69,000 candela smokes everything for throw, but the Arisaka E2ST has about the same total output, at over 500 lumens... the E2ST has pretty much the same throw/candela as the Modlite PLH, but less spill brightness and spill width, but a hotspot of EQUAL brightness and the hotspot is TWICE as large! The E2ST SMOKES the 300 lumen Arisaka/E1 series head, the 300 lumen Surefire M300 head and the Surefire 500 lumen M300 head for output. The runtime on the 16340 INR is 20 minutes at essentially full power, 5 minutes of rapidly dropping power suitable for clearing indoors but not outdoors, and 5 minutes of moonlight mode that starts as a sub 40 lumen taclight and ends as just... better than your cell phone. Over discharge is under 2.5 volts and it was at 2.55 volts at 30+ minutes... so dim it was silly. Not worried about over discharge unless you accidentally leave the light on unattended.
For a purpose built light, I find that adequate runtime. If you can spare the 1.6 ounces and bulk of the Modlite 18350, it certainly has more power available. I will have to test self discharge of the Vapcell INR 800 mah 16340, but its not supoosed to be an issue.
If you want a tiny, ultra light, high output, 100m capable light, that hits with the big boys Modlites, you should give an Arisaka 300 body, 600 head, and Vapcell 16340 INR cell some thought. It works better than I hoped thus far.