In Balance - the Operating System of the AR15 and AR10 Family of Firearms

The AR15 is undoubtedly America's rifle. Whether in military format as the M16 rifle or M4 Carbine or in semi-auto commercial dress, we love our black rifles. There is also no doubt that after more than 50 years, the AR has grown, changed, shaped, and been pressed into service in more ways than Stoner could have ever imagined. Of course, Stoner originally designed the AR as a 7.62 rifle so the changes started pretty early on in the rifle's lifespan. Still, we've chopped and stretched barrels, shortened gas systems, changed receiver extensions and buffer weights, and just about everything else on this modular sweetheart of a rifle. As rugged and reliable as the platform is (naysayers not withstanding) the operating system actually requires a delicate balancing act for optimum performance. Sure, you can over-gas the action to help the rifle eat under-powered commercial or imported fodder, but over-gassing introduces another set of problems altogether.

The Pyramid of Perfection, no... the Triad of Triumph. Um... the Triangle of .... let’s just say that there are three factors that must be in balance in order for your AR to run perfectly. So what are those three things?

  1. Pressure
  2. Mass
  3. Time
The AR15 Operating System Requires a Balance of Pressure, Mass and Time

In the context of this equation, pressure is a function of the ammunition in use, the configuration and condition of the bore, including the position of the gas port, and the environmental conditions at the time of firing, namely temperature, though internal factors can have an effect. Commercial .223 Remington ammo is loaded to lower chamber pressure than military 5.56 ammunition. Even among .223 or 5.56 (or any single chambering) ammo, different models of smokeless powder or different lots of smokeless powder can produce disparate pressure levels and pressure curves. The pressure curve impacts the the level of pressure that remains at the location of the gas port. You'll see a significant difference in the pressures generated by subsonic and supersonic ammo in the 300 AAC Blackout.

A sub-freezing and snowy day on the range spawned the RIFLESPEED line of modular Gas Controls. A rifle that worked perfectly when temperatures were in the low 70s on day one of a two-day rifle match almost completely ceased to function when temperatures dropped into the 20s the next morning. The 77-grain match ammo I was shooting delivered tremendous accuracy, but was on the ragged edge of having adequate pressure to cycle the rifle's action in warm temperatures. Once temperatures dropped, there simply wasn't adequate pressure delivered to the gas port to ensure reliable cycling. If you’re not familiar with the issue, temperature sensitivity in smokeless gunpowder is a very real factor that results in lower internal pressures and reduced velocities at low temperatures. The opposite can be true in high temperatures. This results in the same problem manifesting itself in the exact opposite manner. Extremely high temperatures, due to air temperature, exposure to intense sunlight, or both, can cause pressures within your firearm to spike dangerously upon firing. There have been numerous reports of this issue. As a result, high- and low-temperature testing are now part the adoption and approval process for new military ammunition.

Cold Weather Can Impact Pressure

Every semi-automatic firearm relies on reciprocating parts to complete the firing cycle. In the AR15 the reciprocating mass is composed of the buffer, the bolt carrier, and the bolt, plus the small bits and springs within. There are a number of factors that impact the movement of these parts including; spring rate, coatings, lubrication, wear, or fouling. All of these can impact the reciprocating mass, but from a practical standpoint, the weight of those parts is the most easily manipulated (good or bad) when we want to affect the velocity of the reciprocating components or the timing of unlocking the bolt from the barrel extension.

The rifle buffer used in the M16 weighs five ounces. When we started using shorter receiver extensions on collapsible-stock carbines, buffer length had to be reduced as well. The standard carbine buffer (CAR buffer) weighs just three ounces. Couple the shorter gas system with a lighter buffer and reliability problems surfaced. One of the most common methods used to improve reliability is to increase the weight of the reciprocating parts. Heavier parts resist unlocking longer (remember that whole inertia thing from 7th grade physical science?). Upon firing, the cartridge case expands to nearly mirror the dimensions of the chamber. While the pressurized case is held against the chamber, a significant amount of adhesion occurs. Delayed unlocking allows for the pressure within the chambered cartridge case to subside slightly. This allows the temporary lock between cartridge case and chamber to break as the case shrinks back towards its original size. Once the reciprocating parts begin to move, heavier parts will resist acceleration relative to lighter parts. So far, so good. However, those heavier parts also resist deceleration as the buffer spring exerts increasing force against the reciprocating mass. Herein lies one of the problems of simply making the reciprocating parts heavier. Doing so results in increased recoil as heavy parts are forced to slow, then stop, then resume movement in the opposite direction. Your shoulder is the springboard for that equal and opposite reaction. Increased recoil leads to increased aiming disruption which is a fancy way of saying that while your carbine is recoiling unnecessarily your sights will no longer be on target and they’ll be more off target than they should be.

Finally, time (A better term may be duration) is the third leg of this triangle of balanced performance. The time or duration of system pressurization is based on several factors, but of primary importance are barrel length and gas system length. Shorter gas systems pressurize the action sooner and since pressure is bled into the action closer to the chamber, the pressure level is higher (earlier in the pressure curve). Longer gas systems delay the initiation of pressurization. Shorter barrels allow pressure to escape sooner. Longer barrels allow pressure to remain within the system longer. Just the interaction between gas system length and barrel length requires a balancing act all their own, but in any event, adding a suppressor (silencer) to the the end of your barrel unavoidably increases the the time your action will remain pressurized by delaying the release of that pressure into open air. In fact, that’s the entire point of a suppressor (functionally speaking). The sound of a gunshot is created by the violent discharge of the pressure generated by rapidly burning gunpowder. A silencer slows that release, thereby reducing the associated sound.

Suppressed Carbines are Hugely Popular

When the duration of pressurization is increased, the overall volume of gas delivered to your action increases. If the action of your perfectly configured carbine was previously balanced with the correct reciprocating mass, gas port size and location, adding a suppressor has just disrupted that balance. To restore balance while using the suppressor you can increase reciprocating mass or decrease pressure. Neither increasing mass nor decreasing pressure are practical options for adjustments in the field or on the go, however. Do you carry multiple buffers of varying weights with you in a tactical situation or in the field? Obviously that’s not a practical solution. What you can do in the field, on the go, or in a tactical environment is turn the Control Knob of your RIFLESPEED Gas Control to the correct setting for your evolving situation. No tools are required, settings are numbered, identifiable, and repeatable, and with the built-in rotation-stop feature you’ll never adjust out of the range you’ve selected for your carbine. There are no small parts, no tiny detents, no threads exposed to carbon buildup, and no tiny springs. With the rotation-stop feature you can make adjustments without taking your eyes off your mission. Simply dial to the hard stop then count to your correct setting.

RIFLESPEED Gas Controls offer ideal solution to balancing your gas system in varied situations

If you’ve never experienced the remarkable difference made by a properly regulated gas system, you may scoff at the suggestion of recoil being a factor with an AR in most chamberings. The question is; if you could have ideal performance from your carbine, but with significantly less recoil and aiming disruption than you have now, wouldn’t that be a good thing? Is there any reason at all why you would choose to have a less reliable carbine? Would you want a rifle configured to wear out sooner or have more maintenance issues? Why should you choose one configuration for a specific circumstance when you can be sure that doing so will increase (or guarantee) the likelihood of problems in other circumstances? RIFLESPEED Gas Controls are the ultimate solution for insuring and improving the reliability, shootability, and consistency of your AR15 or AR10.

Add Comment

0 Items