Went out last weekend with a friend and his registered m16 receiver. On a 16" carbine, lightweight barrel with M4 style handguards, multiple mag dumps without any heat issues. 3 mags through my suppressed 10.5", lightweight barrel, KMR keymod handguard w/railscales and it was too hot to hold for the next 20 minutes. Any good suggestions on keymod rail covers to deal with heat (besides gloves)

Paracord wrap

Kevlar sleeve could help. I use kevar lined thin leather gloves when I run stuff like AKs hard.

Pistol grip

A suppressed SBR like that is going to heat up fast with a couple mag dumps. The covers will help a little bit but the heat will still radiate through. Personally I wouldnt add the weight for the rare occurrence you get to play with a full auto lower.

Cheapest option is to buy one of those fabric oven gloves.

Next cheapest option is a vertical grip.

For sustained rates of fire you really need an LMG upper or an upper with quick change barrels like the MCR.

As Spartikis said above, Vertical fore grip is the answer.

You won’t notice the heat, and the bigger benefit is the huge increase in control on full auto.  There is a huge difference between holding the handguard and holding the vfg.  The angled foregrips are not the same.  They don’t help with control on auto.

Another +1 for the vert polymer foregrip.

There is no better solution to the heat buildup.

If you put a bunch of panels on the rail you are just trapping the heat to the barrel.  Eventually that heat is going to soak through whatever panels you put on and any exposed metal on the panels or rail will still burn you if you grab the wrong spot.

The vert grip will also help control full auto mag dumps better in my experience as well.

I personally like the Larue front grips myself, but they are a bit spendy.

It would appear that this range session poignantly demonstrated the vastly different heat-isolating capabilities of polymer handguards, with their heat shields and substantial air gap, and the metal heat-sinks known as railed forends.

Handguards are designed to protect your mitts from barrel heat, and for this purpose, they do an excellent job. They don’t work very well for mounting lights, lasers, or other stuff. If you don’t need/want that “stuff” on your rifle/carbine (aka a “naked” rail with covers), you would be best served by handguards.

Railed forends are necessary for mounting lights, lasers and “stuff”, but their metal construction means that they get hot, and they stay hot. If you need/want to efficiently mount “stuff” on your rifle/carbine, you are forced to use a rail.

Rails are not “better” than handguards; they both have their pluses and minuses. There’s always a compromise to be made.

VFG, as an engineer I cringe at heat shields.  I want that heat conducted away from the barrel/chamber as much as possible, not trapped.  Al handguards with a large barrel nut are actually excellent heatsinks.  Of course you have to plan accordingly.

As an engineer you should realize that heat shields are often necessary and the perfect solution in many applications.

As an engineer I fully understand their purpose and their use and rather like the benefits they have in certain applications.

Heat shields are awesome for the end user.

My coolest running setup is an 11.5" SOCOM with a Knight's RAS. Granted it's not on a MG lower, but you can really keep up a decent fire rate while still holding onto the rail. My uppers without heat shields are definitely less pleasant to shoot for sustained periods without either gloves or a VFG.

I understand why they are necessary.  Same reason some cars have governors.  You are sacrificing performance to accommodate for human fallibility.  Military weapons are designed for the lowest common denominator.  Hence the A2 profile.

If I'm shooting a MG I own though, I will use an Al HG, my head and a VFG so that the HG can dissipate as much heat as possible.

Yes, that's what they are designed to do.  How does this magic voodoo work?  By reducing the heat transfer from the chamber/barrel to the outside.  This reduces barrel life and accuracy though.

Automotive governors are more of a political thing. A feel good measure of uselessness. Heat shields are based in physics and heat transfer.