Category Archives: Tests

AR-15 Rate of Fire as a Function of Buffer Weight and Action Spring – Initial Comparison

I must stress that this is an initial comparison based on limited data points, but I feel that it will be fairly accurate once more data has been gathered.

Many rounds were fired through a number of uppers, but I spent the most time with a 20″ rifle gas upper; data can be seen below. The barrel used had a 5.56mm chamber and a .092″ gas port, which are standard M16A2/A4 features.

Although the BCM action spring and the “generic” action spring were identical in appearance, their performance was quite different. Given the same weapon, recoil buffer, magazine, ammunition, environmental conditions, and even number of rounds in the magazine, the BCM spring reduced rate of fire by approximately 70rpm compared to the generic spring.

Time in each component of bolt carrier travel was reduced, however, the most significant change occurred during the “hang time” where the bolt carrier group was at its rearmost point of travel; the BCM spring delayed forward movement by as much as 35%. In terms of real world performance, the BCM spring allowed 35% more time for the magazine spring to properly feed the “stack” of ammunition.

Even the Wolff reduced power spring slowed rate of fire more than the generic spring. All springs had less than 300 rounds/cycles “on” them prior to testing.

While the switch from Carbine to H buffers resulted in a significant (~50rpm) drop, going from H to H3 – double the weight difference of the carbine to the H – only reduced rate of fire by 6-13rpm. I have many theories, only some of which are grounded in reality. It may be that simply having any amount of tungsten in the buffer changes the way the buffer acts when it reaches the rearmost point in the receiver extension tube, for the average rearward velocities of the H and H3 buffers were nearly identical, whereas other times and velocities differed.

Although I am not ready to release data for other uppers (even on an “initial” basis), their behavior with the above buffers and springs seemed similar.

Before anyone asks, I don’t have sufficient data for the H3/generic spring yet.

Rates of fire were calculated on high speed video, which was calibrated prior to testing. High speed video of my uppers on registered, full auto lowers were used to calculate theoretical rates of fire for semi-auto lowers. Rate of fire reduction is not the only reason to select an action spring and buffer. Your individual results may vary based on dozens of factors.

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Full Auto Fun – Er, Testing

Two quiet, unassuming gentlemen arrived at the range with some serious hardware while I was shooting. Naturally, I pestered them until they let me shoot one of my uppers on a Colt M16 lower.

I was able to take a fair amount of high speed video, which I will be processing a bit at a time…here are two short clips…

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1911 Drop Testing

Although this is the sort of thing that I do occasionally, and have in fact conducted in the past, it is important to note that I had nothing to do with the testing shown below, and am simply reposting it from another location (with permission from the owner of the data). Drake is a law enforcement officer and 1911 gunsmith, and has done some excellent testing here.

1911 Drop Testing
The original testing used a 9mm steel firing pin and a 9mm titanium firing pin. The firing pin hole was then reamed for a .45 sized pin and the tests were repeated with .45 sized steel and titanium firing pins. All of the firing pins were weighed prior to testing. A Wolff XP firing pin return spring was used for all of the testing. All of the cases used for testing used Winchester large pistol primers. The frame and slide were donated by Gary Smith at Caspian. The pistol was built using techniques learned from Larry Vickers and Bruce Gray. The pistol was tied to a section of 550 cord, looped over a pulley, and dropped onto common floor materials. The magazine was loaded with 8 dummy rounds to bring the pistol up to proper weight. Four floor types were selected. Concrete, Pergo, 5/8 plywood, and shag type carpeting. The thumb safety was left OFF as preliminary testing with the safety ON indicated that damage to the thumb safety, slide, and plunger tube would occur with only a few drops. The hammer frequently dropped to the half cock notch during testing.
Firing Pin Weights:
9mm STI titanium pin— 2.17 grams
9mm Caspian steel pin — 4.45 grams
.45 STI titanium pin — 2.36 grams
.45 Colt steel pin — 4.30 grams
I was amazed at how easily a Series 70 1911 could be drop fired. Steel firing pins and concrete are a bad combination. 9mm sized pins and titanium construction will add several feet to your safe drop distance. I will be running Wolff XP springs and a Ti pin in all of my Series 70 type 1911’s.
I have attached an Excel spread sheet with the results. You will notice a lot of “Did Not Drop” entries. I saw no reason to drop test a particular combination of firing pin and flooring if it was not firing at higher distances or on harder flooring. I did several drops at various distances to get an idea of safe drop distances. This was to account for hard or sensitive primers. Each primed case was dropped only once. Just in case you were wondering, the pistol sustained significant damage. The muzzle is distorted from being dropped. I had to turn down the outside diameter of the barrel three times just to keep the slide from locking up. The muzzle, magwell, and grip safety have some serious blending in their future. Nothing sounds worse than a 1911 hitting the concrete from 10 feet!

The Excel file is attached here.

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Does Nickel Boron Reduce Heat?

We’ve been bombarded with a variety of coatings and platings over the past few years, most of which are called “proprietary” and given a cool name. In reality, there aren’t a whole lot of finishes or metal treatments out there. Many are just variations on a theme, such as all the derivatives of nitrocarburization and nickel plating.

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.

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Heat Dissipation: Insulate or Circulate? Gas Tube or Op-Rod?

Standard disclaimer: I’m not a scientist and this was not a scientific test. Any conjecture on my part is purely an uneducated guess.

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.

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Federal XM9HA Chronograph Test

In a recent AR15.com thread, it was claimed that Federal 9mm ammunition identified as XM9HA was a contract overrun of 147gr HST hollow point projectiles loaded to the impressive velocity of 1180 feet per second. That’s 9mm Major territory – and beyond. It was also reported that this ammunition had a high rate of failures to feed or failures to fire in a variety of handguns.

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).

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LWRC IAR Drop Test

I’ve been told that the following information is OK to release. It’s pretty self explanatory. I removed the names of certain individuals, but the information is otherwise unedited.

Land Warfare Resources Corporation
Engineering Memorandum Engineering Memorandum
To: IAR Team
From:
Date Written: 8/8/07

IAR Drop Test – Summary

Purpose: The internal drop testing of the LWRC Infantry Automatic Rifle
was undertaken to determine how robust the Rifle and its component parts
and accessories are and simulates a drop from a rotary winged aircraft at
the maximum height a soldier might disembark from a rotary winged
aircraft or from the top of an Armored Personnel Carrier or Tank. The
purposed was also to find the best commercial off the shelf parts and
accessories that meet the requirements of the USMC IAR Draft RFP.
Testing Protocol: The LWRC Infantry Automatic Rifle was drop tested to
the USMC test protocol to ensure durability of the weapon and integral
accessories and furniture for internal product improvement prior to delivery
of LRIPS for Phase 2 of the Picatinny IAR Solicitaion. The weapon as
tested was 8.5 lbs. The weapon was dropped several times from all
angles starting with 12 o’clock butt down from 1.7 Meters (from the
buttplate) with the stock extended and locked in the 3rd position on the
buffer tube. The surface it was dropped on was concrete covered in 3/8”
plywood. For the purposes of the test, no optics were installed on the
weapon. The first drop being 12 o’clock butt down would test the viability
of the telescoping stock systems in the extended position. The testing
continued dropping the rifle from the 2, 3, 5, 6, 7, 8, 9, 10, 11 o’clock
positions from 1.7 m on the same surface. Back up rear Iron Sights were
in the upright position.
Pass/Fail: Success or failure of any component or accessory was judged
by whether the component was still operable after the drop testing. The
component could be damaged, but the weapon had to remain operable
and the repair of the replacement part must have been within the scope of
practice of a line infantry armorer.
Components Tested: Magpul CTR stock, Magpul MIAD, LMT SOPMOD
stock, A2 Gov Issue Pistol Grip, Latest Generation M4 Stock, VLTOR
EMOD, IAR Prototype Config, Matech Rear BUIS, TROY BUIS (sights are
purely educational as USMC has specified rear sight).
Failures Summary: All buttstocks failed the testing first drop except for
the VLTOR EMOD stock. The VLTOR EMOD stock survived all drops
from all angles and remained completely functional. Examination after the
testing revealed 2 hairline cracks from the corners of the steel locking plate
hole in the polymer. The stock remains completely intact and functional
and the engineering team has determined the stock would not need to be
replaced to serve the life span of the weapon. The Matech Rear sight
body cracked but remained functional. The Troy Sight broke during angle
drops and was rendered non functional. All other IAR Prototype
Components, and the weapon itself were inspected gauged and
measured, then test fired. The weapon underwent 48 drops (far beyond
the requirement) without any functional problems. There were no pistol
grip failures.
Land Warfare Research Corporation

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