I have a suppressor that is covered partially (maybe 1") by a rail, and a Streamlight HLX mounted as well at ~10:00. Whenever I get my suppressor hot, the Streamlight dies. This seems to be the batteries overheating, not the overheating protection circuit, because it stays dead until I replace the batteries. Running Surefire CR123s exclusively.

Surely someone else has run into this with all of the setups I see similar to mine. I really don't want to have to push my light even further back or buy a new shorter rail and a suppressor cover. Is this just a defective light?

Would love to try and help but you need pictures of how the light is mounted.

Thatll do it. You need to offset the light more, move it or get something between them as a thermal barrier.

Yea it’s a real thing a lot of people won’t believe. You might want to use a cantilever style mount to extend the body passed the rail. Having the suppressor tucked inside the rail is notorious for trapping in a lot of heat. The heat may be transferring through the mount and into the body of the light so using an extended mount could be better at having the air in between to act as the vapor barrier and , possibly, help. ALONG WITH...  I can’t remember if the hlx first came out as a dual fuel setup or not. Is this hlx capable of accepting an 18650? Since it starts right up when you change the batteries maybe try using a protected rechargeable. I don’t know if you already use rechargeable batteries or not, but if you have an 18650 charger maybe try an orbtronic 3500mah or keeppower 3500 mah. If your not setup already with a charger and don’t want to spend the extra dough you can go with the streamlight 18650. It has a micro usb charge port right on the battery. If it does not accept 18650’s, maybe you want to try a rechargeable 16650 in either keepower or orbtronic brand. You will still need a battery charger for these and the voltage is less than using 2 cr123a’s so you won’t get the full output. My reasoning for the switch in batteries is that these rechargeables have protected circuitry that will allow them to step down in power so that they will not be damaged. So since there is little you can do about the heat, short of replacing the rail to a shorter one, at least your light won’t completely die on you while using it, maybe, I don’t know. Since the heat radiates up, maybe you could flip the light to the lower half of the rail and use a tape switch. Or you could have a defective light, I can’t say, but these are some things I would try if I were in this situation.

Eta: I can’t spell.

I'm not sure a protected 18650 will help if the problem is heat buildup to the point where the pressure relief blowout fuse gets tripped.

IMHO, thermal isolation is your primary need. I thought of shielding, but all that would do is allow more heat buildup without reducing the ability of the mount to transfer it to the light.

Get your suppressor out from under the barrel.   Your rail is absorbing a lot of heat and its spreading through to the light.  A polymer mount may help insulate it.

..Or cloud defensive, modlite, at the very least surefire could be your answer.

My Surefire is mounted to my suppressor a lot closer than that and I’ve never had an issue. Maybe I need to shoot more.

Of course my light is mounted at 6 o’clock. I catch a lot of crap from people but heat rises, so maybe that’s why I’ve never had an issue.

ETA: not as close as I was imagining after looking at it. Regardless I never have had problems. Run primaries as well.

I really don't want to have the suppressor sticking out of the barrel; this is my HD gun and it's in a quick access AR vault that exposes the rail. It's difficult to take the can off with the QD tab inside of there, and it's almost impossible with the rail flush against the wall when it's in the vault. If I pushed it out and someone were to break in, there could be an NFA item walking away.

Plus it just looks cooler that way.

I'm not sure if the problem is convection from the heat escaping the mlok slots, conduction through the rail and mount, or just a (relatively) inexpensive light that may not offer as much thermal protection as a Surefire.

This generally happens when I get the can hot, like shooting 5 30 rounders in 20 minutes or so. I guess like the old doctor joke, the best solution is "don't do that," but I've seen plenty of videos of guys like Aaron Cowan (Sage Dynamics) and others put that many suppressed rounds downrange and haven't heard of their lights failing, even pushed forward.

I just don't want to dump a lot of money into a Surefire and find out I still have the exact same problem after spending another $3-400 on this gun. Lord knows how much it already cost me.

I think the poster above might be in a better position because it's a 300blk, which doesn't get as hot? And maybe the rail allows for more heat dissipation, combined with the 6:00 position and beefier mount.

I just don't know. Maybe a polymer rail section in the same position and putting the old 1913 mount back on, and some mlok rail cover sections below the light?

I'd play with it and move it back to see how far you'd have to get. Manta makes a handguard wrap, maybe that with a unity tactical fusion (I don't know if it would clear, you'd have to check diameters).

That's a good idea too, mount the light lower as you move it around.

OP, you are correct in that mine above is 300 BLK but I use LilGun which is an extremely hot burning powder. I’ve done 120 rounds in 90 seconds before and while the hand guard was far past what was comfortable to hold the light still worked.

I would test on my .223 with a can but my rail doesn’t cover the can so it really wouldn’t be a good comparison.

If you don't mind a kinda ghetto solution, muffler wrap an inch before suppressor attachment to an inch after the end of handguard should do the trick, and it's cheap.

Can you attach an mlok cover scales so it shields the head of the light from the heat?
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Is your light mount metal where it attaches to the handguard??  If it is, switch to a magpul mount. A metal mount will basically turn your flashlight into a heatsink.

From OP's description, it sounds like he's cooking the batteries till their blowout fuse pops and destroys the cells. Breaking a direct conduction path as you suggest is a good direction to explore. I'm really curious if any of the polymer options will survive the heat.

Of course, it looks like OP has a dedicated weaponlight with an integrated mount. Are there any alternate mounts that mate to this light's built-in mounting points?

It uses any standard scout mount.

If anyone were to break in, they'd just take the whole damn thing not just the suppressor. Only other option worth trying is going to be the polymer rail section. I've done the whole suppressor tucked under the handguard thing - it sucks. If you ever take a carbine class with that setup, I guarantee you'll change that rail next day.

It's in a Shotlock vault, not laying around.

Does the handgaurd get uncomfortably hot to the touch when the light exhibits the behavior you describe?

I'm not a fan of covering cans with rails, partially for this reason.

Another thing you can do is use a magpul polymer mount as it will transfer less heat from the rail to the light body. Mainly though,  I think you need to consider how hot the can gets, how close the light is, and the heat tolerance of cr123s. It seems like you've done at least cursory due diligence to determine that:

Heat is causing this
You're using quality batteries
It's the battery, not the light/circuitry

Straight forward: keep your batteries cooler.

Try a thorn tail mount? You can have the light in the same spot but the mount would be further back.

You dont even have anything on the last mlok section of your rail. Get a rail 1 section shorter. Your grip, BUIS, everything does not use the last rail section so get rid of it, lose weight, have a cooler rail and functional light. Problem solved.

And I think cans inside rails do NOT look cool, LOL! Especially ones that require manipulation of a tab or collar. Looks like an ignorant newb didnt think about the manipulation required to remove the can. Never thought someome might see that as a feature.

i have had issues with streamlights getting too hot and not turning on/shutting off, one on a surpressed Ar and one hand held one while working in an attic, was 110 outside and prob 140 in there but if i can work it I sure as hell need my light to.  I switched my long gun light to a surefire mini and never had the issue again, same with my work light.  Have a couple streamlights on my handguns and have not had issues there.