Nickel boron is related to electroless nickel plating and electroless nickel with teflon (also known as Robar’s NP3) with regard to the plating process. Nickel boron is reported to provide “permanent dry lubricity”. In other words, less friction amongst the reciprocating parts, as well as where they interface with static components.

It didn’t really occur to me that this might lead to lower operating temperatures. In fact, when I noticed a discrepancy between a rifle with a nickel boron BCG and a similar rifle with a standard, phosphate finished BCG, I wasn’t sure what to think. They used different rail systems and gas system lengths. Initially, I chalked it up to those minor differences. Then, I decided to use a standard BCG in the rifle that was originally equipped with the NiB BCG, using the same test protocol. After that, I repeated the test, twice, with each BCG, allowing the weapon to cool to ambient temperature between strings of fire.

The test was performed by firing 80 rounds of centerfire ammunition as quickly as possible through the AR-15 pictured below:

No malfunctions were experienced during any of the 5 strings of fire.

I then measured the temperature of the gas block, chamber, bolt face, and handguard (in four locations) immediately after firing and at two minute intervals out to 10 minutes.

For the sake of comparison, I have included the temperature of an M4 type carbine equipped with a KAC M4 RAS handguard. The rifle above was equipped with a Daniel Defense OmegaX 9.0. None of the rails had any covers during the testing.

Gas block temperature profiles were nearly identical for all weapons.

The same goes for chamber temperatures.

Bolt face temperatures, however, were another story.

The bolt face of the nickel boron plated BCG stayed, at its peak, 13 degrees cooler than the same weapon with the standard BCG, and 17 degrees cooler than the M4 carbine with the KAC M4 RAS.

Here is the nickel boron BCG compared with the POF RDIK and POF P-415 uppers, which underwent the same test (again, we’re talking bolt face temp here):

As always, I’m not a scientist and this was not a scientific test, but I do feel fairly confident in the results, given that I double and triple-checked the numbers and nothing was outside of a small margin of error. The above numbers are the average of said tests and retests.

I do realize that this was a sample size of one and that the limited testing doesn’t definitively prove anything. I do think that it is an interesting result that I would like to follow up on after I get more ammo and possibly more nickel boron plated BCGs.

As I’ve written before, POF-USA provided me with two of their upper receivers – one is of their standard P-415 design and the other is actually operated via a standard gas tube. It’s called the RDIK.

This gave me the opportunity to compare how each handled heat. That is, just how effective are all the design changes POF has made to the AR receiver, barrel nut, and handguard? Well, as I found out, they’re quite effective. However, that test was pretty limited – only 30 rounds per weapon – and I wanted to step it up a little.

Today I put 80 rounds through each of three ARs – the P-415, the POF RDIK, and an M4 type AR with double heat shield handguards – and will shoot more in the next few days with other weapons. I also took chamber and bolt face temperature readings, in addition to the handguard temp (average of 4 places on the handguards) and gas block/barrel temp.

The rounds were fired as quickly as possible, and the rifles were left with the bolt carrier group in the forward and locked position. Temperature readings were taken immediately after firing and at two minute intervals thereafter, out to 12 minutes post fire.

We’ll start with handguard temperature.

As you can see, the M4′s double heat shield handguards were much hotter than either POF offering. The POF RDIK, in fact, had a slightly cooler handguard than the POF P-415.

This was in part due to the very hot gas block of the P-415. Here are those temperatures:

It wasn’t quite as scorching as the M4′s 353 degrees immediately after shooting, but it was over 320. The POF RDIK was drastically cooler – it never exceeded 200 degrees.

Chamber temperatures were much closer for all weapons.

The P-415 did stay cooler than the RDIK, with a difference of  roughly 10 degrees. The M4 was hotter than either of the POF weapons, due in no small part to the heat sink barrel nut used on the POF rifles.

The following graph shows bolt face temperature.

It would appear that a large portion of the heat reaching the standard AR-15′s bolt comes from the front – that is, the chamber. If we compare chamber and bolt temperatures, the RDIK and M4 hardly ever had more than a 2 degree difference between the chamber and the bolt (with the bolt normally being 1-2 degrees cooler than the chamber). The P-415 bolt, on the other hand, generally stayed about 10 degrees cooler than the chamber.

What does this all mean? Well, to me, it means that getting the heat out (circulating air) is more important than trying to keep the handguards cooler (insulating the barrel with double heat shields) – regardless of the operating system you choose. It would appear that the piston/op-rod P-415 does slightly reduce bolt face temperature – but the RDIK does a very fine job of keeping the chamber area cool in its own right, which in turn keeps the bolt cooler.

It seems that there is no free lunch, and the heat which is not present in the P-415 chamber and bolt is very present at the gas block. The heat sink features and wide open handguard with lots of cooling slots almost seem necessary to keep the barrel/gas block temperature relatively in line with that of the M4 type AR. I would really like to test an op-rod conversion that does not have the heat sink barrel nut, big handguard, etc.

I would assume, based on these graphs and the comparison of the three uppers, that the large majority of the temperature of an AR-15 bolt during sustained fire can be attributed to the “fire in the barrel”, and a minority comes from the gas which circulates through the action. In other words, with the piston/op-rod system, the chamber “heats” the bolt, whereas in the standard operating system, the bolt is heated not only by the chamber but in a small way by the gas coming through the gas key, which in turn causes the bolt to pass some heat back to the chamber. As a result, the temperature of the bolt and chamber on a standard AR are married to one another to a greater degree (ha, ha) than on the P-415.

Again, I’m not a scientist. If anyone has a better conclusion based on the above data, I’m all ears.

I was recently sent a small quantity of this ammunition for testing via a chronograph. It was requested that I use a Glock 19 as the test firearm.

Although I only fired 10 rounds through said Glock 19, I did not experience any failures to feed or fire. Unfortunately, I also did not experience anything approaching the claimed velocity. The fastest round was 1009.42fps, the slowest 973.06fps – with an average of 992.56fps.

For comparison, I also fired 10 rounds of Winchester Ranger Bonded 147gr through the same firearm. The high was 992.21, the low 963.15, with an average of 974.8.

If you can acquire this XM9HA ammunition for a fair price, and it functions reliably in your firearm, it would appear to be adequate ammunition. However, I wouldn’t expect 9x23mm performance from this cartridge. As a side note, recoil felt pretty tame compared to my 115gr handloads at 1200fps (which are not particularly hot to begin with).

We often see comments about how light barrels heat up too quickly. This is partially true – a lighter barrel will generally heat up faster than a heavy barrel. The “too” part is where the problem lies. Too fast for a machine gun barrel? Most likely. When you’re putting out a sustained rate of fire that can reach several hundred rounds per minute, a light barrel is definitely unsatisfactory. However, if you have a rifle, and not a machine gun, a lighter profile barrel may not heat up “too quickly”.

Also, there are many comments about how cool piston/op-rod systems run. These comments seem to be applied liberally and generally; that is, you will often hear that all piston conversions “run way cooler” than standard DI weapons. However, it’s not as if the mere presence of the op-rod has a chilling effect on the barrel, which is a critical component of the rifle, to be sure.

So we have two schools of thought here: that a lightweight barrel profile is more appropriate for use on a carbine, and that the standard system of operation is not unnecessarily hot; and that a heavy (or fluted/heavy) barrel is more appropriate for use on a carbine (or maybe a carbine machine gun to be used for laying down suppressive fire), and that an op-rod allows the rifle to run cooler.

Recently, while doing some experiments with standard plastic handguards, I thought I’d also compare a civilian legal M4 clone, or close to it – a Spike’s Tactical M4 LE with a Knight’s Armament M4 RAS handguard – with two Patriot Ordnance Factory rifles. One is a P-415, which uses POF’s op-rod system, and the other is called the RDIK, and it uses a gas tube, just like a standard AR-15. However, it’s equipped with the same heavy fluted barrel, heat sink gas block, reinforced upper receiver, and single piece railed forend that the P-415 uses.

To complete this test, I fired 30 rounds of 5.56mm ammunition through each rifle, then measured the temperature of the handguards in four separate places, as well as the temperature of the gas block/barrel. I measured these temperatures immediately after firing, 1 minute after firing, 5 minutes after firing, and 10 minutes after firing, using an infrared thermometer. I also measured the temperature of the bolt face immediately after firing.

Here are the handguard temperatures:

Note that all three handguards got progressively hotter until sometime after the 5 minute mark. I found it interesting that the POF gas tube upper was within several degrees – up or down – of the P-415 op-rod upper during the whole exercise. I also found it interesting that every handguard had reached essentially the same temperature 10 minutes after firing.

Here are the gas block/barrel temperatures.

I was surprised to see how cool the POF RDIK gas block was after firing. There was a greater initial temperature difference between it and the P-415 gas block than there was between the P-415 and the Spike’s M4 LE. In addition, the M4 cooled faster than the P-415, as you can see, though each upper had roughly the same temperature loss profile after 1 minute.

This proves an often-overlooked point: while light barrels do heat up faster than heavy barrels, they also cool down faster than heavy barrels – apparently, faster than even a heavy fluted barrel. This also proves true a comment made to me by an industry professional while we were discussing this topic: that the gas block of a piston/op-rod rifle gets very, very hot.

As a side note, the temperature of the M4′s bolt immediately after firing was 94 degrees; the P-415′s bolt temperature was 88 degrees. The RDIK’s bolt was 89 degrees.

Although this was a very limited and rather unscientific test, it would seem that the vast majority of the POF rifles’ cooling ability comes from the heat sink barrel nut, handguard, fluting, etc, and not from the piston/op-rod system. I will do more extensive testing in the near future.

Here are the handguard temps:

And the barrel/gas block temps:

Not only did the M4 RAS transmit less heat to the shooter’s non-firing hand, it also allowed the barrel to cool faster than the plastic handguards. This is in addition to its other benefits, such as mounting various accessories.

Today, I tested the Magpul MOE handguards using the same protocol: 28 rounds fired in a rapid manner, with temperature measurements at specific locations and time intervals.

The MOE handguards have a single heat shield. By that, I mean a single heat shield. The “single heat shield” handguards have one heat shield in each of two handguard halves, and the double heat shield handguards have two heat shields in each of two handguard halves. The MOE has one heat shield in the lower handguard half, and no heat shield in the upper half. This might sound bad from a “protect the user” standpoint, but it has many more vent holes than the other handguard styles, and these holes are located to draw in cool air on the bottom and expel hot air up top.

As to the effectiveness of the design, I’ll let the results speak for themselves. I was pretty impressed. First, the handguard temperature averages.

And here are the gas block/barrel temperatures.

Based on the results of this limited test, it seems that the MOE offers a very good compromise between reducing heat transmitted to the user’s non-firing hand and allowing heat to escape, resulting in slightly faster barrel cooling.

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.

He’s recently completed an exhaustive test of a Bravo Company 14.5″ M4 type upper receiver assembly. You can read the details here. In essence, he stripped away all lubrication, replaced critical items in the lower receiver, and proceeded to shoot 2400 rounds through the weapon with only magazine-related failures (he used USGI type mags to simulate as closely as possible the military M4).