There are two primary types of gas systems for the AR-15. They are DI and Piston. DI stands for Direct Impingement. DI is the original design whereas the Piston only became popular in recent years.
DIRECT IMPINGEMENT VS PISTON
The AR-15 operates by transmitting hot gas behind the bullet into the gas tube at which point it the tube uses the gas to either move a piston or deliver the gas directly back (direct impingement).
No matter how the force is applied, it makes the bolt unlock, move back, eject the spent casing and push a new cartridge into the chamber.
By and large, most AR-15s are DI instead of Piston. Like most things, there are pros and cons to each.
PROS OF PISTON
Typically more reliable in poor weather conditions (dust, water, moisture, heat, et al.)
Relatively cleaner as dirty gas is vented out
CONS OF PISTON
More expensive than DI
Heavier with more weight in front
Harder to find proprietary parts from manufacturers
Less accurate than DI
Unless you’re in an Arnold Schwartzenegger movie where you have to fire your weapon coming out of water or you live in a desert somewhere, a DI system will be perfectly adequate for most purposes.
Assuming you properly maintain your AR-15, a DI model will be a dependable weapon.
DI GAS SYSTEM LENGTHS
Gas system length is the distance to the gas hole. The gas hole refers to the triangular front site base (FSB) that sits on top of the barrel.
Although there is the rare “Dissipator” model that has a sixteen-inch barrel, the rifle length gas system is normally used for an eighteen-inch barrel.
The average choice for sixteen-inch barrels is a carbine or midlength gas system.
Personally, I favor the midlength system because I think it’s advantageous because it enables the user to have a longer sight radius when you’re using a front sight base. You also get more rail space because the handguard extends from the upper receiver to that front sight base.
We’ve mostly been talking about the FSB (Front Sight Base) style gas block here where the front sight is combined with the gas block and there’s a reason for that.
I always recommend this style to first-time shooters because it’s easier to have a front sight and it’s affordable to use a non-free-floating barrel.
Another good thing about this style is that it can be converted by grinding down the front sight base to allow for a free-floating barrel.
Front sight blocks generally use non-free-floating handguards. So the two-piece handguard touches the barrel at the front sight base which, unfortunately, can add a bit of inconsistency when it comes to force. Consequently, your shooting accuracy can be affected.
Nevertheless, if you are a non-competitive shooter, the non-free-floater will be accurate enough.
While there are some aluminum models, most are made from polymer and are cheaper and just as good at more affordable price points.
Magpul MOE handguards are our go-to handguards because they enable the shooter to attach Picatinny rails on slots which allow you to add accessories. Picatinny rails are a tad on the heavy side, but if you like to attach accessories, this is the way to go.
BCG (BOLT CARRIER GROUP)
The BCG is basically the engine which runs the AR-15. It retracts when you pull the charging handle back.
When you let go of the handle, the bolt carrier group moves forward, strips a round from the mag and releases a round into the chamber.
When you pull the trigger, the hammer is released and it strikes the firing pin, hitting the the primer. This sparks the gunpowder, sending the bullet down the barrel. This is where the gas system comes into the picture.
THE BEST AR-15 MANUFACTURERS
There are a number of other factors that you’ll want to consider when selecting your AR-15.
They include build (precision build or 18” barrel vs pistol build or short-barreled rifle), optics, trigger (single stage vs two stage trigger), rifle type (semi-auto vs full-auto), but for the sake of brevity, let’s get right down to it.
Below is a full list of all the top AR-15 manufacturers around followed by my personal favorites.
These are the manufacturers that seem to be reputable rifle vendors who don’t cut corners and commit to providing quality materials. Either that or they’ve just got a crazy marketing budget that makes them look boss.
TOP TIER MANUFACTURERS
As of the publishing of this article, we vouch for the following eight companies as the absolute best manufacturers of AR15 rifles:
Lewis Machine & Tool
Yankee Hill Machine
The companies listed above are believed to be the greatest sources for service grade AR-15s.
Smith & Wesson
These are some companies with good guns that are fine for training/range plinking purposes. I suggest you run at least 1,000 rounds through one of these rifles before you trust any of them with your life.
You want to know that your AR works before affording it the title of great home defense weapon.
Don’t be thrown by the title, these are perfectly adequate manufacturers with perfectly good guns. They are inexpensive and may be the right choice for starter rifles.
Palmetto State Armory
Rock River Arms
When it comes to the top tier, you should be prepared to spend no less than $1,000. On the other hand, most mid-tier manufacturers’ rifles start at $500.
$1,000 might sound steep, but keep in mind that you’re paying for quality, name, and the research and development that goes into the same.
OUR TOP PICKS FOR THE AR-15 (UPDATED: 2017)
Let’s talk a bit about my top picks!
Aero Precision is a well-known name among people who build their own AR-15s, but they’ve also done an incredible job of offering complete AR-15s with unique features. Their AC-15M is a handsome gun with a sixteen-inch barrel that we simply love because of its ergonomics and price.
The Aero Precision AC-15M is great for first-time shooters because it won’t cost an arm and a leg and it’s got most of the bells and whistles that can also be found in some of the more expensive options.
The M-15 is a lightweight tactical carbine and at $1,000, it’s one of the better defensive AR-15s on the market. Tailored to front line users, it can also cut the mustard as a home defense weapon.
A bit larger than the last piece on this list, the M-15 has an eighteen-inch match-grade, Cerakote-coated stainless steel barrel. A semi-automatic, the M-15 is durable, compact and ultra-fast.
All three options are worth looking into, but we like the Mod 0 more because we’ve spent more time with it than others. The Mod 0 is a 16” 5.56x45mm rifle that typically goes for around $1,100.
With a chrome lined barrel, the Mod 0 was not designed for the gamer, rather it is geared toward tactical applications. But when it comes to training and range shooting, this one packs a lot of punch.
This one includes the aforementioned Magpul MOE handguards and a PNT trigger. For me, it’s the gold standard of modern AR-15s.
The Mod 2 is a quarter of an inch wider than the Mod 0 and shares its cable lock and 5.56mm chambering. It’s also got a mid-length gas system that enables it to run cooler than its counterparts.
The Recce 14/16 is more pricey than the others on this list, generally retailing for $1,500. But it’s a beautiful, streamlined weapon that will definitely be the envy of everyone you encounter at the gun range. The first time I picked one up, I felt like I was in a Predator movie. Seriously, just look at this design:
As with the Mod 0 and Mod 2, the Recce 14 is a 5.56mm caliber rifle with a chrome lined barrel and 11595E certified steel. It’s got a Mod 4 charging handle, a Mod 3 pistol grip and a BCM QD end plate.
With a shot peened bolt, feed ramp flat top receiver and chrome lined bore and chamber, it’s a real beast.
4. COLT LE6922
Another semi-auto, the LE6920 M4 carbine is a versatile option that is known for its performance and accuracy. With a wide range of ammo options, this tactical rifle also has a chrome lined barrel with a 1:7 rate of twist and combat-proven power.
Often implemented in law enforcement and military operations, the LE6920 has six lands and grooves, a 20-round removable magazine and a 5.56x45mm NATO chamber. At 6.95 lbs, it’s not the lightest of rifles, but it’s certainly a sweet piece.
The DDM4 has a 16-inch cold hammer forged barrel and a vertical foregrip for ideal manipulation. This one is good for maneuverability which makes it a nice pick for a CQB rig.