Convoy M21C Review – with Osram CULPM1 & 8A driver

This content originally appeared on Reddit on April 24th, 2021.

The Boring Stuff

I purchased this light from the official product page on the Convoy Aliexpress store. Price at time of writing is $38.39

There are several variants of this light. At the time of writing it’s available with 6 different emitters, 2 different drivers (12-mode-group & 4-mode) and 3 different body colors. There’s even a side switch version with a smooth ramping firmware called the M21C-U, but it only has one emitter option at the moment.

Size

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver
MeasurementOfficial (mm)Measured (mm)
Head Diameter5555
Body Diameter2828
Tailcap Diameternot specified29.5
Length163162
Bezel Inside Diameternot specified43
Lens Diameternot specified51
Lens Thicknessnot specified2
Reflector Diameternot specified45.75
Reflector Lengthnot specified40
Reflector Hole Diameternot specified9

What comes in the box?

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

The box is excellent. Everything here is purposeful and Simon didn’t waste any money on printing or fancy opening mechanisms. It’s just a sturdy, plain cardboard box with a foam insert and a sticker on one end telling you the model & configuration of the light. This packaging is perfect. Just what you need and nothing you don’t.

User Interface

The 8A linear driver used in this light has Convoy’s “12 Mode Group” firmware installed on it. It’s very similar to Toykeeper’s “Biscotti” firmware Convoy has used in the past. It gives you 12 different mode groups to choose from and allows you to enable or disable mode memory.

StateActionResult
offhalf-pressno action
offclickon (mode memory optional)
onhalf-pressnext mode in group
onclickoff
on20+ half pressesconfiguration mode

Changing mode groups or the state of mode memory is a little too complicated to get into here, but it’s not hard to figure out and becomes second nature once you’ve done it a couple of times. Check out the official product page if you want more info. I find I like mode group 4 with no memory the best. It goes 1%-20%-100%-strobe-bike flasher-battery check-SOS.

In the next firmware version I’d like to see the 0.1% mode replaced with a 0.01% mode. The 0.1% mode is probably about 5 lumens with this emitter & driver and I’d really like a sub-lumen mode. I’d also like to see a shortcut to 100% (preferably a quick double tap) that can be enabled or disabled just like mode memory. The ability to disable all the blinkes except battery check would be nice too, but they don’t really get in the way.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

Output & Regulation

Lumens: I have no way of measuring lumens, but I think 1400lm is a reasonable estimate for this emitter & driver combo.

Candela & Throw: With a fresh cell, I measured 275,000 candela (1048 meters) using my smartphone and the Ceilingbounce app.

Levels: Below to the right is an output graph showing the levels from the default mode group (group 1): 0.1%-1%-10%-35%-100%. Mode spacing in all the mode groups I’ve tried is pretty good.

Regulation: Below and left you can see an output test with cells at three different voltages. There’s very little output loss going from 4.2V to 3.55V. Unfortunately output at 2.85V isn’t nearly as high, but that’s to be expected. Low voltage protection has kicked in at that point anyway.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver
Regulation test (left) and mode test (right)

Runtime

These tests were performed in a closet with the Ceilingbounce app on my phone. I used a fully charged Molicel P42A for every test.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver
Complete runtime (left) and first 15 minutes or so (right)

Total runtime is just over 90 minutes. Thermal stepdown happens slowly and smoothly over about 11 minutes. From there, output is pleasantly stable and lasts until just before the 80 minute mark. At this point, output drops smoothly for a few minutes and then low voltage warning kicks in. Output continues to drop and the light finally shuts off completely at just over 90 minutes. When the test was over I measured cell voltage at 2.85V.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver
35% runtime (left) and 20% runtime (right)

35% output looks fairly well regulated. There’s some slight thermal stepdown over the first half hour or so. That output lasts until just after the 90 minute mark when brightness begins to steadily decrease. There is a low voltage warning right at the 100 minute mark. Output continues to decrease steadily until the light shuts off just before 110 minutes. 20% output looks similar, just longer, lasting to about 190 minutes.

Build

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

This is one of my favorite looking lights, tied with the Noctigon KR1. I chose the M21C over the L21A specifically because I think it looks worlds better. Build quality is excellent. The anodizing is just lovely. All the edges are broken over. Texturing on the body is nice and grippy without being overly aggressive. The head is heavy which probably helps a lot with thermals. It also makes it feel like a mallet when you hold it like one. The cooling fins are thick and deep. The stainless bezel is hefty and makes the best nicely-machined-metal sound when you unscrew it. The threads between the head and the body tube are the smoothest and quietest I’ve ever felt. The threads between the body tube and the tailcap are very nice as well.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

Contrary to the official product photos, the tailcap spring did not come bypassed. This is also the case on my Convoy Z1 with the same emitter & driver. The spring feels nice and sturdy though, so I don’t have any reason to think it’s not up to the task.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

It feels pretty good in hand. I find that in what I’m going to call a “normal” grip, my thumb rests on one of the flat portions of the head and it’s quite comfortable. My thumb wishes there was a side switch there though. In a reverse grip, my fingers want a little more body tube length to hold onto and I end up resting my pinky on the “collar” of the head. Accessing the switch in this position is fine, but it’s not as comfortable as I would like. A cigar grip works about as well as a reverse grip, just differently. Switch access is significantly easier. However, with how heavy the head is, it can quickly get fatiguing to hold the light like this.

My only significant issue with the quality of this light is the centering ring which just doesn’t do its job very well. More on that later.

Emitter & Beam

This variant of this light has an Osram KW CUPLM1.TG emitter (known by Hank from Intl-Outdoor as the W2.2, known by Vihn from Skylumenas the W2.1) and a smooth reflector. I think that’s an excellent combo for this host. It throws very well and also provides some nice spill.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

Looking at the light itself, the emitter appears to be fairly well centered, but the beam shots tell another story.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

The beam isn’t as clean as my Noctigon KR1 with a CSLNM1 (W1) emitter nor my Fenix PD32 V2 with a CSLPM1 emitter. The corona is really uneven, more so than should be expected with a rectangular die. It’s not something I notice when I’m outside actually using the light, but it bugs me when looking at the beam on a white wall. The PD32 V2 has two perfectly symmetrical flower petals of corona, which makes sense. The KR1 W1 has four perfectly symmetrical flower petals. The M21C has three that are each a different size.

I disassembled and reassembled the head several times to try and get it centered. I even sanded down the centering ring slightly as suggested by another user, but it didn’t make any difference. If I place the ring on the emitter manually and try and move it slightly, I can feel it moving a little bit which is probably what’s causing the issue. I’ve heard of this issue on other Convoy lights using the CULPM1 so I’m inclined to believe it’s an issue with the centering ring Simon is using. It’s a real shame because this is a great host, great driver, and great emitter, let down by something as small and inexpensive as a plastic centering ring with too much tolerance.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

It’s a joy to use outside. It seems to throw for forever but is still quite useful only a few feet away thanks to the bright spill. The tint on this emitter is neutral and pleasant. Even the color temperature looks to be warmer than the expected 6-6500K. You can really see the intensity difference between this and the Noctigon KR1 on the right.

Batteries & Charging

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

This light officially uses an unprotected 21700 cell. I did most of my testing with unprotected flat top Molicel P42A’s. I did try a 30Q and it worked, but it rattled a lot and jostling the light would cause it to cycle to the next mode. I experienced no such problems with a P42A. There are no forms of charging available with this light, which is a plus in my book. There are no fiddly rubber flaps to deal with.

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

The positive contact is a brass standoff so button tops or flat tops would work. Even some of the proprietary cells we’ve seen recently would probably make contact. I’m not sure whether a protected cell would fit or not. My P42A’s are 70mm long and I was able to stick one 3mm magnet on the end with no problem, but two magnets was too long and I couldn’t tighten the tailcap all the way.

Switch

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

The switch is OK. I don’t particularly like reverse clickies in general, but this one is fine. It’s very tactile and clicky. Convoy sells a very cool metal lighted switch that’s compatible with the M21C. You can also get a forward clicky switch from Mountain Electronics that should work with it. I’ve got one coming in the mail so I’ll give it a shot when it arrives and update this accordingly. I do wish Simon offered an official forward clicky switch on his store though. I’d also like a little but more accessibility for the switch. The raised wings on either side that allow for tail standing are fine, but the valleys in-between aren’t cut down far enough and they still interfere a little bit with switch activation.

Conclusion

r/flashlight - Tactical Grizzly's Convoy M21C Review - with Osram CULPM1 & 8A driver

What I like:

  • Gorgeous and well made host
  • Great emitter & performance
  • Great driver

Improvements I’d like to see:

  • Official forward clicky option and a little more room to access the switch
  • An improved centering ring that’s more precise to make the corona cleaner
  • A lower lowest mode & a shortcut to 100%

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