This is going on a 6.7 lb. AR15, I would like it to be durable, light weight, and have good throw. Spill is less important and I carry extra batteries so run time is not a huge issue.
Thanks!
Just how much throw do you need? The M600C that I have was notably more powerful than the M300A. Also, the M300A is said to run for 1.4 hours or some such embelishment, and yeah, I guess it does, but it drops out of regulation very quickly in my experience (owned one). The M600C will stay in regulation for +- 90 minutes.
Now, as to throw, the M600C I have has thrown equal to, or out-thrown every 6P module I have (XP-G2 LOP reflector by Nailbender, 5000K 375-ish OTF, XM-L by EDC-Plus 440OTF, those are the two meanest ones) EXCEPT! for my XP-G2 SMO reflector by Nailbender. It has nearly twice the lumens (half the run-time in regulation), and a near identical beam profile, and out-throws it by what I consider a noticeable but realistically insignificant margin. Maybe another 10-15 meters?
The M600C as it sits with an RDS and good darkness should be a 80-110m light depending on your vision.
I dumped the M300A and went M600C because it, to my eyes, looked like a 50-75 lumen boost, probably came close to doubling my regulated run-time (surefire's run-times are "until it drops to 50 OTF lumens"), and only added about 1-2oz, IIRC. The extra length of the M600C goes forward, so it doesn't matter to me. Even on my 10.5" SBR, it is a safe distance from the muzzle mounted on the end of the 7" VIS rail, based on the mock-ups I have done with measurements (SBR still in jail) on my 14.5" setup, so the length is kindof "free". Barrel is there, anyway. The weight is only a bit.
Now, I guess none of this helps you do anything with your M300A, but what I am saying is that on 1 CR123, you are going to be very limited either on power, or run-time, and definitely both compared to a 2-cell, which for size/weight is "free" for our application as outlined above.
After all my playing around, I am running the OEM KX2C head.
Your other option is to wait for this alleged 250 and 500 lumen scout, or buy the already released 500 lumen X300U.
Barring that, I would try to find an oldschool M30 malkoff and run the VME head, that will give you throw that is pretty similar to an OEM M600C, although my M600C does out-throw my Malkoff M60 by a slight margin.