This is one of the items on “the chart” that a lot of people gloss over – especially if they want to replace the standard handguards with some sort of railed handguard.
So, I don’t expect this article to get a whole lot of attention. Also, please note that I am not a scientist and this is not meant to be a scientific test.
However, I was frustrated with the progress of another project while at the range, and decided that a few mag dumps would raise my spirits.
Here’s how I conducted this test:
A Smith & Wesson 5.45x39mm upper with CAR type single heat shield handguards was placed on a standard lower. I recorded the temperature of the handguards in four locations, using an infrared thermometer, before any shooting was conducted. These four locations were the forward- and rear-most vent holes on the top and bottom of the handguards.
Then, I fired a magazine (28 rounds) of 5.45×39 surplus ammunition through the rifle as fast as I could. I recorded the temperature of the handguards in those four locations immediately after shooting, 1 minute after shooting, 5 minutes after shooting, and 10 minutes after shooting. I originally intended to measure the temperatures past 15 minutes, but they bottomed out and dropped very slowly after 10 minutes, so I didn’t see that it would be very valuable data. Between measurements, the rifle was laid ejection port cover up, with the bolt locked to the rear, as required by range regulations.
After the rifle was allowed to cool a sufficient amount, I replaced the handguards with M4 type oval handguards that had double heat shields and repeated the above process.
Here is the average of the four locations. Temperature is measured in degrees Fahrenheit:
As you can see, there was a drastic difference between the two handguards initially, although it narrowed after a minute or so, and the single heat shield handguards did shed heat faster than the double heat shield handguards. Interestingly, the double heat shield handguards actually got slightly warmer after a minute or so – the extra shield kept the heat in rather than allowing it to come out all at once, for lack of a better explanation.
One more note – the double heat shield handguards delayed barrel cooling. Here is the temperature of the barrel at the front sight base:
Again, this is probably because the double heat shield handguards didn’t allow the heat to dissipate as quickly as it could.
Based on this limited testing, I would recommend double heat shield handguards for those who want to keep heat away from their non-firing hand, but aren’t as concerned with barrel temperature, and single heat shield handguards for those who are more concerned with allowing the barrel to cool as quickly as possible. On the other hand, for the latter purpose, a free float handguard designed to dissipate heat is probably the best option.