This guide will help you choose an AR 15 barrel for an upgrade or buy for a new build. This video covers barrel length, twist rate, and gas system length. Part 2 covers muzzle device choice, round lethality / range, barrel material, and chambers.
The most common AR-15 barrel lengths are 14.5″, 16″, 18″, and 20″. I prefer 18″, or 16″ for maximum velocity without excessive length or weight. 14.5″ barrels have legal concerns and must have a pinned flash hider, compensator, or muzzle break, which I do not recommend. 14.5″ guns also don’t have enough velocity IMO, especially for 5.56 NATO.
Barrel Twist rates:
1 in 7 (1:7), 1 in 8 (1:8), 1 in 9 (1:9) are all discussed. A shorter twist rate, 1:7 provides the most aggressive twist allowing the heaviest bullets (77 grains) to be effectively stabilized. 1:9 works with 55 and 62 grain bullets, but should go beyond there. 1:8 works with 55-68 and some people use 77 grains. Excessive twist can negatively affect very light bullet accuracy and insufficient twist will not stabilize heavier bullets.
Gas system length.
The three common AR15 gas system lengths are carbine, mid, and rifle length. I do not recommend carbine length gas systems with 5.56 since it provides no real benefit and I find the ergonomics poor. A mid length gas system is best for a 16″ barrel since it makes the gun easier to shoot and handle. The longer gas system typically also has a longer handguard, improving ergonomics. For a 18″ or 20″ barrel gun you want a rifle length gas system. This will be very easy to shoot, provide a very long hand guard gripping surface, and generally be awesome.
**Correction**
I said gas pressures increase over barrel length, which is incorrect. Gas pressures are highest in the chamber and decrease over time/distance. The bullet does still pickup velocity with longer barrels, but the pressure slowly decreases.
However, the advice given still stands. Longer gas systems are often softer shooting and generally regarded as more reliable. I just explained that part really wrong.
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I have a Windham Weaponry VEX. It has a heavy 20in SS fluted bull barrel. This rifle is really accurate way more accurate than I need. I don't even hunt,but I may have to start if this inflation doesn't let up. 😆 I don't really know what I'd hunt with it cuz you can't hunt deer with anything less than a 6mm bullet in my state. I guess I could hunt deer with my 9mm Ruger American pistol. 🤣
Wiki is bias trash..
It's not the weight that effects the twist its the length of projectile which typically get longer with weight
Weight has nothing to do with it. It is the length of the bullet that makes you need the 1/7.
Good stuff, I'll have to finally pull my ruger out of the box and hope it has some of the favorable attributes you have mentioned before I start building it.
Please understand that the majority of aftermarket shorter barrels and gas tubes make your build overgassed and slightly out of time. Not to the point of leaving swipe marks on the case head, but much more gas pressure than required. Using and tuning an adjustable gas block is a requirement for peak reliable operation. Much less force exerted on your locking lugs, faster cyclic rates that actually stay in time, and less felt recoil.
Want to see a blank stare?
Ask an “expert” how tube length effects the cyclic timing
The background music was annoying as I tried to listen to you.
Shoot the mil spec gun. It’s been worked out for all considerations. The A4 is best for a multitude of reasons: better velocity, better sight alignment, and better shooting from prone position.
I have a smith and Wesson M&p 15t with a 16 barrel but it doesn’t have a brake on the barrel do I have to buy another barrel or can I mount a brake on it ??
Anyone who cares, has an adjustable gas system
Easy, longer means better, higher twist rate means better, get away from the AR platform because Direct Impingement isn’t the way to go.
بلا بلا بلا
Overall, this was a good video. I would advise against calling something "stupid" or "dumb", particularly if you don't have a full understanding of the why. Gas system length is unrelated to handguard length.
You can use a any length handguard with a carbine, mid, intermediate or rifle length gas system. As you correctly stated, you should ensure that the handguard covers the gas block, or you risk knocking it out of alignment, which will affect the function of the rifle. It's for this reason I'm not a fan of "railed" gas blocks like the one on the DPMS Oracle.
Longer gas systems aren't "more" reliable, they can be less, which is one of the reasons why the military uses a carbine length. Carbine systems are a bit more violent and cause accelerated wear on some parts, particularly on the bolt & gas key.
The reason for the enhanced reliability of a carbine length gas system as opposed to a mid-length gas system is DWELL TIME. This is a function of the amount of barrel left after the bullet passes the gas port. Once the bullet leaves the barrel, the gas pressure drops precipitously, so more barrel after the gas port allows gasses to travel down the gas tube to the bolt carrier. With a mid length gas system, the block is further out, there is less barrel before the bullet exits…and thus less propellant gasses to cycle the bolt.
This does cause less of an impulse making the mid gas system a bit more pleasant to shoot, but let's be honest – the 556 is a soft round anyway.
If your ammo is full powered, you shouldn't have reliability issues with a mid length gas system, but with lower powered ammo like steel case Wolf and Tula, some have had cycling issues. It's a trial and error thing- but life on the line, I want something I don't have to think about, so carbine gas system is better…..NOT DUMB.
Read up on how dwell time effects cycling of the firearm. I'm not knocking you, as I needed to study it quite a bit. Just a little info for you. Keep up the vids!!!
I thought it was length of the projectile and not the weight that determines twist rate.
Why does the handguard need to be tied to the gas system? Can't you have a really long handguard on a shortlength gas system? Granted short gas system is really bad idea for 16 inch barrel.
Nice video. 👍🏼
I've been looking into building an AR15, most descriptive and helpful video i've seen
There is nothing at all "stupid" about a carbine gas system, plenty of shooters like the carbine handguard length, you may not but it probably is the most popular length, carbine and rifle were the two military original gas lengths, mid-length is civilian. Not that many shooters want or need a rifle with that much barrel and hand guard length such as 18" and 20, hunters maybe, also the military used 20" because of bayonets, which now only the Marine Corps trains for.
Terminology- twist rate spin stabilizes the bullets. 1 in 12 is faster and 1 in 7 slower spin rate. A model to show people is a bolt with a nut in it. Thanks for making the vid.
20" is not a monster 24" bull barrel….is a monster
So, so long as the barrell is min 16 then no matter what it doesnt need to be pinned and welded?
Good content, thanks!!
Really great video and spread of information covered. Could not catch it – did you mention 55gr and 1:7 twist rate?
Carbine gas systems don’t clog up after prolonged use. The gas block and gas tube get hotter than mid length, which clears them out. Also the higher pressure helps them operate in adverse conditions. So if you’re fighting with your rifle outdoors, or shooting long strings of fire, a carbine system will go bang more before you start to have malfunctions. Probably why the military uses them.
Also, a 14.5 barrel is easy to pin and weld, then remove and pin and weld again if you need to. The loss in velocity is minimal and it’s a lot more maneuverable. Probably why the military uses 14.5.
Yes, if you’re opposed to a little extra work/cost to pin and weld your barrel than go with the pointless 16” (this rifle was never designed for 16”). Yes, if you are never planning to run your rifle dirty, or put reliability before comfort, go with a mid length gas system. To say neither is useful is wrong.
Auron figurine in the back, I'm listening
Just got my first one….18" barrel….
It is tested fact that some ammo actually looses velocity over 18 inch and even 16 inch on some as well. Under 13 inches, most 5.56 and 223 ammo does not perform as designed due to the velocity needed to cause the boolit to open up as a hollow point or can cause tumble or over penetratration due to falure of the jacket to cause a boolit to open up which turns your AR into a great performing 22 magnum. A 13 inch AR is fine up to about 125-150 yards depending on barrel and ammo used. The U.S.Army went with a barrel length of 14.5 inch with an A2 flash hider as their ideal length field rifle after starting with the 20 inch barrel. For me, a 14.5 with a wielded pinned A2 flash hider, medium contour barrel, bringing the overall length to 16" , 1 in 8 or 1 in 7 twist barrel, has a winning combo of handling, weight, and performance and I can use any stock I like as well as not working about the ATF or state governments deciding to again, restructure language for the “pistol length AR15 laws”, which they can and will do with political pressure.
Thanks in confirming my thoughts, f the bull on other comments, much appreciated on your time and knowledge.! Thank you sir
Excellent information! But I found myself constantly rewinding because you are talking pretty fast
Thanks for the vid, I was a little worried about buying an 18" barrel cuz im only 5'8 and i thought it might be too big.
carbine gas system master race
18 inch 1-7 twist rifle length gas system. Aka a Daniel defense ddm4 v11 pro
You don't have to pin a muzzle device on a 14.5 just build it as a pistol and use a pistol brace
You go brother, nerds know our stuff
I swear to god, the federal government can suck my fucking dick!!!
Sorry, I should have read the other comments before shooting off my big mouth.
Actually the further a bullet goes down the barrel the less gas pressure you have. A longer barrel does give a larger muzzle velocity because the gas accelerates the bullet for a longer time. You have a fixed amount of powder that will burn into a fixed amount of gas. If this gas is in a smaller volume ( bullet close to the receiver) you get a higher pressure. When the gas is in a larger volume ( bullet near the muzzle) you have a lower pressure. So, when you port the gas system further down the barrel you get a lower pressure. The pressure may be lower but it is still high enough to get the job done.
I like this dude LOL 'that's just stupid' I totally get it!
what barrel and upper do you have on your long range 20 inch setup ?
Great video i learned alot thank you sir
You have twist backwards…. slow twist is for larger weight… faster is for your lighter bullets…
I have spikes 16in 1:9 looking for some good reloading vids and any idea with help with building some pillls
Hello, i'm new to building an AR and i just ordered a 16" carbine length barrel 1:8 twist and along with it i also picked up a carbine length gas tube with low profile gas block. . . did i order the right match? thank you in advance.
If your a smaller guy like me a canine length is perfect. Keep your ammo dry