Selecting an AR barrel
In my previous experiences combined with my time at gun stores, I have come to understand some basic truths about AR barrels and wanted to share this information for all to use while making decisions about ARs. It’s the most important part of an AR, and understanding the differences in barrels and the realities of the choices makes the choices easier. The characteristics important to understand about barrels primarily break down into the following categories: how they are made, what metal they are made of, and the quantitative differences in barrels. Quantitative differences are aspects like length, twist, and contour.
Barrel production breaks down into multiple forms of forming the rifling and the contour. There are multiple mechanical ways to complete these tasks, but the long and short of it a barrel is either cold hammer forged (CHF) or not. The CHF process compresses and elongates the barrel blank while a rifling form is inside a drilled center hole. The end result is a more dense steel in the barrel. All other processes essentially cut the rifling out of the barrel. The easiest way of comparing the two is forging a knife blank vs removing metal to make a knife blank. Both work, but the forged steel is more dense and stronger. There are advantages and disadvantages to both, but with modern engineering techniques neither CHF nor not CHF barrels are what I would consider a defining aspect of barrel quality. The basic differences are CHF barrels handle heat better, last longer, and can be lighter for the same stiffness. In 5.56, this could be the difference of 5000-10,000 rounds of barrel life.
Barrel material is another shades-of-gray area in barrels. 4140, 4150, Chromium molybdmum vanadium (CrMoV), Stainless steel (SS), coating this, non-coating that… You can get seriously lost in the metallurgy and chemistry of the metals and coatings out there. Unless you are building a very specific rifle, don’t get too wrapped up in these aspects. The average shooter isn’t going to see the differences from one type of material or coating to another with a few exceptions. CrMoV barrels are very tough and take wear very well. Stainless Steels (there are roughly 140 different mixtures of SS) are softer (some are just barely softer) but are typically more accurate overall than CrMoV barrels. These are generalities and truly a matter of scale. The scale is just how much more accurate and is the difference in accuracy relevant in return on longer barrel life. A dedicated prairie dog gun may very will benefit from the accuracy aspect of SS. Target shooting and man sized silhouettes out to 400 yards, the difference in accuracy isn’t relevant and the longer life of CrMoV makes it a better choice.
Barrel coatings come down to two areas, the inside and the outside. Inside the barrels, you basically have chrome lined and ferritic nitrocarburising coatings. The most commonly used ferritic nitrocarburising coating in barrels is melonite. There are other coatings, but these are the two most common coating found inside AR barrels right now. Chrome lining has been around a very long time. It’s tried and true and chrome inside chambers renders a coating with viscous properties. If you run a lot of steel cases, stick with chrome lining. Melonite is really tough stuff and primarily used to add longevity to the barrel’s rifling. On a very small scale and in general, Melonite seems to be slightly more accurate than chrome lining. In my experience, both work but I have ran into barrels with melonite coatings that caused the chambers to be slightly too tight to headspace gauge. This is more an issue of the production process and less on the actual coating. External barrel coatings are basic. If not SS, it needs to be coated with some basic process to stop rusting. If SS, it really doesn’t need a coating. Much like how the rifling was made, materials and coating can be argued till you are thoroughly confused or thoroughly disgusted. I personally fall into the category of chrome lined for general use and SS non-lined for long distance accuracy. Melonite barrels can be good, but I wouldn’t specifically seek one out over chrome lined. A good example of this would be if one should pay $200 for an Aero melonite coated barrel of $290 for a Daniels Defense chrome lined barrel. Both are good and the difference in shooting them will show very little difference in accuracy. The DD barrel will last longer though. It’s CHF, CrMoV, and chrome lined. Very tough stuff.
Individual characteristics of AR barrels are the stuff of lifelong ongoing debate in the category of 9mm vs 45 ACP. If I had a dollar for every time I heard 1:9 twist barrels suck, I could take a week off from work. Twist rates for some reason have become the thing of myth instead of what they really are; a measurement. In this case, they are a measurement of what bullet will fit the barrel when it comes to stabilization. Faster twists (1 twist for every 7 inches, 1:7) stabilize longer heavier bullets than slower twists (1 twist for every 12 inches, 1:12). Think of this as your pants waist size. Like pants, you have a leg length size too. This is the part of bullet stabilization that some miss. The length of the barrel also comes into play for stabilization. Longer barrels stabilize for more twist regardless of twist speed. A 24” 1:9 barrel stabilizes better than a 14.5” 1:9 barrel. I have a 20” HBAR 1:9 barrel that shoots 77gr bullets very accurately. In general, 1:9 barrels of shorter length don’t like bullets heavier than 69gr. It really isn’t the weight, but the length of the bullet the twist rates do or don’t like. So, to muddy the waters even more, a gilded copper round of lighter weight but longer length will favor certain twists differently than a lead core round. Sometimes the weights of bullets are misleading as to why one isn’t shooting well and another is… Seriously, this is just scratching the surface and getting off topic. What is important in barrel selection and twist is the task the AR is being made for. In most cases, 1:7 or 1:8 will cover anything you want to do. It’s generally a safe place to be and only specialized equipment should deviate from these. 1:9 in a 16” or longer isn’t terminal by any means.
Barrel length… The more I research this topic, the more I understand how overthought this aspect of AR barrels is. There are relationships between barrel length and accuracy, stabilization, etc, BUT there is only ONE direct link between barrel length and shooting: velocity. Bullets can only accelerate while in the barrel. Once the bullet leaves the barrel, it’s can no longer accelerate and can only negatively accelerate (for those of you who took college physics) or what the non-nerd world calls decelerate. The velocity difference between a 16” barrel and an 18” barrel can be roughly 100fps from 5.56 NATO ammo like M855. It can be at little as zero from other ammo. Every study I have read concerning barrel length and velocity had come to the conclusion that velocity loss is linear (straight line chart, y=mx+b) and is rarely over 30fps per inch, usually somewhere in the 15fps per inch after 16” of barrel. This makes only specialized uses require specialized barrel lengths. For the most part, a 14.5” or 16” barrel is going to be able to do 95% of the shooting tasks an AR may be employed. Smaller targets at longer distances, longer barrels rendering every little bit of velocity possible helps flatten the trajectory. Short barrels are lighter and easier to maneuver and at times the lack of velocity is advantageous. The MK-18 is a 10.3” short barreled rifle and specifically made for short range, urban type, home entry tasks. I personally think the best overall length of an AR would shake out at a 12.5” barrel, but thanks to the legal restrictions 14.5” pinned is the most realistic for overall use. 16” if you don’t want to pin the flash hider. I don’t recommend 5.56 barrels shorter than 10.3”. They are a fucking bitch to tune and get running, they tear up suppressors like taking a blow torch to the baffles, and cause huge fireballs of concussive deflagration at the muzzle. I don’t recommend barrels past 24” either. At a certain point, barrel length actually slows the round due to gas volume in the barrel.
Barrel contour. This effects three things; weight, heat tolerance, and harmonics. Did I mention weight? Ya, weight. WEIGHT!!!!! If you are ever going to carry it for more than 5 minutes at a time, weight is the most important of these three aspects of barrel contour. Thicker barrels absorb and dissipate heat better and are stiffer so they have a tendency to be more accurate with a wider variety of ammo. I won’t go into the “why’s” of either of these in this, because they are topics in themselves. The weight of carrying an AR at a class all day, even with a decent sling system, rapidly clarifies just how important barrel weight is. I had a 6lb AR that I built for my daughter. She’s all of 5’1” and a buck fifteen wet. Her rifle has a 16” light weight mid length gas DD barrel on it and after I shoot it, I always ask myself why I have anything else in contour. It’s just as accurate as my 20” HBAR and almost the same velocities. It does get hot fast though. In the end, most contour difference in AR barrels happen between the gas block and the muzzle. Everything else is pretty thin unless you specifically purchase a heavy barrel contour. Once again only specialized uses benefit from heavier barrels. (See a trend yet?)
Barrel calibers. AAAAAHHHHHH! I won’t discuss pistol calibers here. Different discussion as their barrel requirements are different. Here comes the caliber debate. This is about AR barrels, keep that in mind. As it stands, 5.56 NATO, .233 Wylde, and 300 Blk/Whisper are the only three chamberings I would think about. Ya, ya, 6.8 SPC, 6.5 Grendle, 458 SOCOM, and all the other super specialized and highly expensive calibers are out there. They are all a pain in the ass to get to run and require extensive money into the gun and into the ammo. For the most part, the specialized calibers have been tried and died (or are dying). DIE 6.8, DIE!!!!!! .223 Rem barrels in an AR are problematic, DON’T DO IT! 5.56 NATO for everything and .223 Wylde for long distance barrels. If you can’t use a standard bolt and a standard mag, don’t think about the caliber. If you do, expect lots of frustration and expense. If you want a 7.62x39 AR, buy a 300 Blk or buy an AK. Yes, I’m opinionated on this topic for a reason. I see the suffering. Nothing like dumping a couple or three grand into a specialized caliber paperweight that costs the same as a new baby to feed and care for. Don’t do it.
300 AAC Blackout. I left this as a separate short topic as it’s becoming more and more popular. It’s a cartridge in it’s infancy (in comparison to others). It’s the legitimized version of 300 Whisper. I like it, but ammo is expensive especially if you don’t reload. Ballistically, it’s really close to 44 special for the powder burn rates, amounts and bullet weights. No, it’s not exactly like 44 special, but close enough one can approximate that the cartridges barrel length is optimum at pistol lengths. 8.5” to 9” barrel length is very good for this cartridge. If you are running subsonic rounds through a suppressor, this barrel length really shines. If you are going to hunt with it, most states require a 16” minimum barrel length. It’s doable, but you are exceeding the amount of barrel you are getting acceleration. I don’t really like the 300 Blk barrels that use carbine length gas systems. They can be too hard to get to cycle completely. The cartridge is revolver mag powders in revolver mag amounts. Very different production of gas to get the system to run. stick with a pistol length gas system.
So, I have rattled on for pages now about barrels and even skipped some info to keep this short. What does it all mean? It means most aspects those contemplate about AR barrels are semantics once you choose one or two barrels. A 14.5” or 16” barrel made by a reputable manufacturer with a 1:7 or 1:8 twist will cover all but long distance shooting/specialized use ARs. CHF barrels will last longer and be lighter than other makes of barrels. In general, SS is more accurate than chrome steels, the question is do you really need the minor addition of more accuracy. If still confused, you really cannot go wrong with a CHF chrome lined 14.5” or 16” barrel made by FNH or Daniels Defense of any contour or gas system length for general overall use. Long distance shooting, get a 20” White oak Armamant or Noveske SS barrel. Kicking in doors for SWAT or Merc work, a 10.3” DD or 8.5” 300 Blk are good choices. The barrel is the heart of the AR. Don’t skimp on it. Spend the extra money for a good barrel. There are some cheaper alternatives to DD and FNH. The one I like are the Aero (Ballistic Advantage) barrels. They are a lesser barrel though.
You get what you pay for. Cheap barrels means they cut corners. Here is my basic standard for a barrel. I want to see a makers mark, the chambering, twist, and barrel material in the barrel marking if at all possible. The more the barrel markings deviate from this, the more likely you are getting a piece of shit. Granted, you order a custom barrel from Kreiger or Lilja, etc, you know exactly what you are getting and the barrel markings are not an issue. You order a barrel online (friends don’t let friends order AR parts on line) and you might be getting a piece of conduit pipe. I have twisted loose the barrel extensions from more unmarked barrels than any other type. This is why they are cheap, skipped critical steps in the manufacture. I don’t recommend KAK, SAA, or Rainer barrels (or bolts). I have had to trash all three and they regularly fail headspacing.
I know I skipped info. To many, the most minute aspects of barrels are relevant to their shooting. Most of the time it’s semantics. Highly specialized ARs do require different barrels, but like any tool, the degree of specialization is only necessary if the end use is specialized. Lastly, barrels are perishable commodities. If you shoot enough, you will replace an AR barrel. Those are good days.
http://www.gunsandammo.com/ammo/pair...st-rates-ammo/
http://www.bergerbullets.com/twist-rate-calculator/
http://rifleshooter.com/2014/04/223-...friends-rifle/
http://www.thetruthaboutguns.com/201...-and-accuracy/
http://www.dtic.mil/ndia/2010armamen...hilipDater.pdf
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Originally Posted by henpecked
