Frequently Asked Questions

Mil-Spec and Mil-Standard Explained

In the firearms industry you hear the term Mil-Spec thrown around quite a lot. Let’s talk for a minute about exactly what the term means. A specification is a standard to which the end user, in this case the US Military, wishes something to be made and held to. The primary reason for this is consistency and interchangeability. Within that realm, and for what the Military Standard covers, there still remain a vast span of places and areas to “tighten up” if you will.

Let’s take a look at a few of those places…The barrel arguably needs to be a very consistent and well-tuned part of the rifle. The Military Standard here, for 14.5” and 20” 5.56 barrels, requires consistency of .0010 from front to rear. Here at CORE®, nothing less than .0003 will make it through our inspection process which is more than twice the Military Standard in tolerance. Indeed, that inspection process itself is 10x tighter than what the military requires, which is a 10% inspection rate. We inspect and test fire 100% of our complete guns, no questions asked. Beyond the barrel, in getting to the action, simply keeping within the guidelines of Mil-Spec conformity is not enough for us. Going above and beyond, both in fitment, finish quality and internal parts, we do everything possible to take the AR-15 platform to the next level. This shows through in the accuracy, consistency and durability of our rifles. But don’t take our word for it. Find your nearest CORE® Authorized Dealer and see if you don’t agree.

Twist Rates Explained

One of the biggest single leaps in firearms technology came in the mid-16th century when it was discovered that imparting spin to a projectile greatly increased the accuracy and range. Ever since that time ballisticians and engineers alike have debated endlessly the merits of one twist rate over another for a given caliber, projectile, and distance. Over the last 20 years, advancements in technology and production have given us unprecedented capability to fine tune our barrels and twist rates.  Thanks in large part to the work of those aforementioned intellectuals, there is very little mystery in choosing a twist rate for your next .223/5.56. The single phrase to keep in mind is “the heavier the bullet, the faster the twist rate needs to be”. For the all around shooter, a 1:7 or 1:8 twist rate will stabilize virtually all commercially available projectiles for the .223 and 5.56 NATO. If you plan to do quite a bit of shooting with very light, fast projectiles (varmint hunters take note), moving to a 1:9 twist barrel would be an excellent idea. For the majority of shooters to whom the .223 and 5.56 NATO bullet weights begin and end at 55 grains, any of the above will work wonderfully. The one shooter that truly needs to take note of twist rate is the long range, heavy bullet enthusiast (64 gr or heavier). For that type of shooting, one of the faster twist rates are a must. While entire books have been written on nothing more than twist rates and the ensuing stabilization, we sincerely hope the above has taken some of the mystery out of selecting a twist rate for your next project. Keep in mind if the rifle you prefer is not listed with your ideal twist rate, we are happy to customize. If you have further questions, please see your nearest CORE® Authorized Dealer or contact us directly.

Gas Impingement and Gas Piston Operating Systems Explained

If there is any one subject in the AR-15 community that has folks talking, it is certainly piston driven operating systems. While still relatively new to the scene, piston systems have definitely garnered plenty of attention. The first and most obvious question to those new to the subject… just what is a piston operated AR? To answer that properly, it’s best to first step back and take a close look at the original concept, direct gas impingement. In direct gas impingement operation, a small hole is drilled through the barrel, where upon after the bullet passes by a small but potent portion of the still-expanding gasses are vented through and into a stainless steel tube. At that point the gasses are directed back to the action itself, driving back the bolt and cycling the action. While battle-proven and highly reliable in its own right, the basis of direct gas operation puts a tremendous amount of heat and no small amount of fouling directly back into the action itself. If kept clean and properly lubricated, this system will continue to cycle and function for many thousands of rounds. With a piston-operated system, the same hole in the barrel exists and the gasses vent through it in turn, but that is where the similarities end. In place of the stainless steel tube is a solid, machined rod of steel (commonly referred to as the op-rod). When the gases vent to the gas block, they interface on a plunger around which the op-rod is fitted. The steel rod, running across the same space that would be otherwise occupied by the gas tube, interfaces on the bolt carrier. When the gun is fired the expanding gasses push the rod back in turn acting upon the bolt and thus cycling the action. Any excess gas is vented off at the gas block itself, well in front of the action and the shooter. This system is cleaner in operation and has a markedly different recoil pulse or “feel”. The main aspect to keep in mind when comparing these two variations is that both are solid, well proven systems in their own right, each with its own strong points. In deciding which one is right for your application, just know you can’t go wrong either way. If you have any further questions, the answer is as close as visiting our web site or your nearest CORE® Authorized Dealer.

Difference Between .223 Remington and 5.56 NATO

The 5.56 mm NATO chambering, known as a NATO or mil-spec chamber, has a longer leade, which is the distance between the mouth of the cartridge and the point at which the rifling engages the bullet. The .223 Remington chambering, known as SAAMI chamber, is allowed to have a shorter leade.  Using commercial .223 Remington cartridges in a 5.56 mm NATO chambered rifle should work reliably, but generally will not be as accurate as when fired from a .223 Remington chambered gun due to the longer leade. Using 5.56 mm NATO mil-spec cartridges (such as the M855) in a .223 Remington chambered rifle can lead to excessive wear and stress on the rifle and even be unsafe, and SAAMI recommends against the practice. Some commercial rifles marked as “. 223 Remington” are in fact suited for 5.56 mm NATO, such as many commercial AR-15 variants and the Ruger Mini-14 (marked “. 223 cal”), but the manufacturer should always be consulted to verify that this is acceptable before attempting it.

Carbine and Mid-Length Explained

The debate between Carbine and Mid-Length systems has raged for quite some years. The first thing to understand is that there is no right or wrong answer – simply advantages and disadvantages. As you’ve seen here at CORE®, we’re willing to cater to either preference. However, a little insight and education on the differences may help in your decision. The primary consideration when choosing either way is overall length of the barrel. The operative measurement here is the distance from the gas port to the crown of the muzzle. This is the amount of barrel that remains after the bullet has passed the gas port and is thus forcing high-pressure, high-temp gasses into the action. This is commonly referred to as dwell time. Having the gas port closer to the crown, as with a mid-length system, reduces dwell time and thus lessens the total volume of gasses forced back into the action in cycling. The advantages here are a moderately reduced recoil pulse, overall smoother operation and reduced wear on parts, with the trade-off being very slightly reduced reliability under extreme or exceptional conditions. As for carbine-length systems, that dwell time (again, heavily dependent on overall barrel length) can be significantly higher. The carbine-length system will force more gasses back to the action over a longer duration, barrel lengths being equal. This imparts more force to the key and carrier, thus cycling the action quicker, with more authority and with an exceptional level of reliability, though the trade off comes in the form of an increased recoil pulse and lightly exaggerated parts wear over time. As you can see, neither system stands head and shoulders above the other. They are simply two variations of an operating system that gives the shooter one more option to tune their weapon to a specific usage. Hopefully this quick explanation has given you an idea of what those are, and will help you decide on which system is best suited for your application.

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