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Barrels for custom AR-15s, Part 1: Barrels are the foundation rifles are built upon. Due to no fault of the barrel maker, AR-15s often don't deliver their accuracy potential.

As a former military armorer and current custom AR-15 gunsmith, the questions I'm most often asked are: How many rounds is my barrel good for before it shoots out? How far should I jump my long range 80 or 90 grain boat tail bullets? What barrel should I buy? I've written dedicated articles for the first two questions. This article answers the last one.

Military shooting team armorers and gunsmiths should be able to answer these questions and have data to back it up. Even if that answer is, "Barrel wear is extremely variable and no one can accurately predict wear out," which is the only correct answer to Question #1. Most team armorers have machine rests and other equipment available to test barrels without the influence of human error that is inevitably involved with shooting from bench rests and other methods, so they should have answers with data. Shooting teams go through barrels and ammunition in great volumes with captive, skilled marksmen disciplined in recording data. If armorers are doing their jobs, they darn well better be asking often! Active duty teams can be more regimented, with leadership able to check things daily. Reserve teams lack this daily contact but still able to glean much more data and experience than civilian gunsmiths.

Most civilian gunsmiths are "general purpose" and work on a variety of firearms. My hat is off to you guys as your range of knowledge is amazing! However, this can't create the depth of knowledge that a team armorer can acquire on a specific platform, monitoring hundreds of guns shot by dozens of highly skilled shooters over the course of many years. The "general purpose" gunsmith will likely have a more limited, part-time exposure to any particular gun.

Having written exclusively on AR-15 topics in this magazine for several years now, I get a fair number of questions and it seems many gunsmiths only see a customer's AR-15 rifle anywhere from once a month to once every year or so. As a rule, general gunsmiths only see "sick" ARs so their opinions can be skewed accordingly. There are a handful of us specializing in the Stoner platform and those that do may rival the full-time military gunsmiths in volume of output but our customer bases are scattered so we usually have limited feedback. Once the gun is put on the truck we may never hear from that customer again until his barrel shoots out or a problem crops up. Email helps, but feedback is still limited compared to team armorers.

There are two general types of custom AR shops. One caters to the growing "tactical" clientele and the other to National Match Course competitors. The tactical shops are more into fancy handguards with rails, flat tops with all sorts of electronic sights and fold down iron sight backups, muzzle compensators, bipods, fluted barrels, etc. I believe "cool factor" cosmetics are stressed more on those builds.

Despite sometimes lavish claims from tactical builders, NMC builders probably stress accuracy more. It is not uncommon for NMC custom shops to offer two general barrel grades with a low cost (usually button rifled) and a higher priced (frequently single point cut rifled) option. I don't know of any shop stocking all of the many brands of custom barrels on the market. Of the dedicated NMC custom shops, it's common to offer either Douglas or Wilson for low cost barrel choices. Although the Wilson usually runs less money, my tests show the Douglas normally shoots tighter groups and last a bit longer. Those custom shops offering a premium barrel option typically choose Krieger. Few custom shops, tactical or NMC, have machine rests to objectively test and compare barrels for accuracy. Testing guns takes time away from filling orders and building guns.

Gun writers occasionally have useful information on the Black Rifle. Most fall into two camps, much like gunsmiths. There are more guys that are general purpose, writing about concealed carry handguns one month, African elephant rifles the next, and shotguns for grouse in the next issue. Since those authors don't specialize they know a little about a wide variety of guns but don't have in-depth knowledge. "General gunwriters" tend to rely a lot on literature searches and sometimes their articles read like parrots rehashing what other writers said before them. Unfortunately, most folks don't have the time, resources, and money necessary to do real field research. This often results in "Encyclopedic Error" where something never proven by any valid research is just repeated so many times that it becomes accepted as true. If a guy is routinely writing about various firearms, how many AR rifle barrels could he possibly test at length? Most of these scribes must be awfully good shots, given the photographed test groups, yet seem absent from formal competition where this skill can be measured. General gun writers are forced to accept anecdotal stories and the item featured in the next issue becomes the "flavor of the month" even though the writer could never test enough to make statistically valid assumptions or conclusions.


Of writers dedicated to the AR-15, Derrick Martin's The Complete Guide To AR-15 Accuracy is excellent, as is Glen Zediker's The Competitive AR15 and The Competitive AR15 Builders Guide. Both discussed barrel choices in their books. You will find the three of us in general agreement on most topics most of the time. This is not because we rehash what the others have written. Derrick and I were military team armorers and competitors in addition to serving in combat. All three of us have conducted valid research with many test rifles over a long period. The conclusions are right regardless the researcher that reached it.


Finally, the barrel makers are obviously an ideal source of information on this. These guys do this every day for a living. Of course, all of them will insist their particular barrels are best, however, you can harvest a great deal of useful information from them. Just remember that making barrels is very different from testing them.

Mystery Barrel Saga

As I've discussed before, the first steps I took as armorer for the Army Reserve Marksmanship Program was machine rest testing all of the team's NMC uppers. It was obvious they had a hodgepodge of barrels from different makers, many of them unmarked. The uppers had been built and serviced by armorers from a different, competing team. I inherited no spare parts or barrels, initially had no purchase budget, and knew we needed new barrels when we did. Test data was kept on serial numbered uppers so as to identify barrel brands shooting the best.

I figured I had the makings of a pretty good start on a barrel study if I could simply link the barrel manufacturers to the groups. I asked the original builders which barrel brands were used and was told they kept no such records. I named them "mystery barrels." This lack of record keeping was the beginning of a huge wake up call for me. As I asked around, I found other team armorers would often use whatever was available. Most of them were experimenting around with about four different brands with little overlap with one exception. Krieger was the one brand used by almost every team.


Initially, I was flabbergasted that teams could have been in business so long and not know what barrels shot best. Poor record keeping was obviously part of the problem. Then I thought about my own military education. While the military does a good job with simple instructions ("Front Toward Enemy" on a M18 Claymore mine, for example) troops rarely learn statistics or how to set up scientific studies, the sort of approach needed to evaluate barrel accuracy. My degree from Penn State is in Wildlife Management. I never took a college course on how to evaluate barrel accuracy, but did take courses in statistics, biometrics, and how to set up a study. The math, research, and science skills needed to manage a deer herd are similar to those needed to evaluate rifle barrel accuracy. As Abby Sciuto famously said, "Science is poetry; it's about making order from chaos."

Paradigm Shift

Risk Is Our Business, the title of Star Trek's James T. Kirk's autobiography, sums it up. I knew that deciding the Army Reserve Marksmanship Program should begin from Square One and be the lead on unraveling the barrel accuracy mystery which others with more resources had failed to discover had us embarking on a paradigm shift. The USAR Team, the "Damn Dumb Reserves," had always been followers. Our defeatist attitude had always been, "Let the big active duty teams figure it out and we will copy them." While a "wait and see" attitude is safe, it created a huge lag. Not only was there the expected delay in waiting on others to conduct research, there was deliberate lag in that information trickling down to competing teams. If you were in charge of a competing team, would you be anxious to release information to other teams that would put them on a level playing field with you? Or would you tend to hold that information closer to keep any equipment advantage in your corner?


It was obvious to me that other members of reserve component teams were also dissatisfied. In "AR-15 Sub-Caliber Training" (October 2015) I mentioned that reserve training centers used to have basement ranges for rimfire shooting, such as the M261 .22LR conversion for the Ml6. While a great idea, this was often under utilized. A group of Army Reserve marksmen assigned to the Small Arms Readiness Group at Fort Gillem, Georgia updated this idea through the 1990s with the Laser Marksmanship Training System, replacing the M261 with a laser simulator. These same SARG folks stepped forward to train troops for deployments in Bosnia and Kosovo and then again to Iraq and Afghanistan. In addition to developing an inexpensive simulator suitable for reservists and conducting training for issue small arms and accessories at Power Projection Platforms for all deploying personnel, team shooters reinvigorated use of the M14 when it was identified as useful for longer range engagements.

These deployments revealed that most military personnel are not as proficient in marksmanship as needed. An idea labeled Squad Designated Marksmen was implemented as a partial solution by having at least one member of a squad trained to a greater degree of marksmanship proficiency. Especially with an optically-sighted M16A4 or similar, this person could shoot well past typical qualification distance and cover a previously requiring a school-trained sniper or support weapons.


My reason for digressing is that knowledgeable taxpayers should have some say in how government spends your money. A top-notch marksmanship program, along with all its members, competitions, and the classes they teach, can be well funded for the price of one cruise missile. SARG was disbanded shortly after the mass mobilizations greatly slowed, so the handwriting is clearly on the wall. Our leadership is already forgetting lessons learned in the Gulf and de-emphasizing marksmanship in our military again. Sadly, if the bean counters ever end up abolishing shooting teams there will be no one with the needed skills to get your sons and daughters up to the necessary marksmanship level needed to save their lives in combat. However, continued effort by shooting teams--especially between deployments--helps keep this knowledge alive and growing.


Conduct Of Testing

When I finally had budget money to start buying gun barrels to test, I recalled a urban legend that was sometimes repeated during that time. Supposedly, some successful shooter (I don't remember if his discipline was ever identified in the story) would purchase ten gun barrels for his rifle from an inexpensive barrel maker, test all of them, keep the best two, and sell off the other eight at a slight loss. As reported, his theory was this would more likely find a great barrel instead of paying double for a premium barrel and taking his chances. I can't confirm if there is any truth to this, but it's plausible due to the relative ease of installing and removing AR barrels. In testing I also stuck with the ten barrel minimum, not because of the urban legend but because statisticians say a sample size of ten is about minimum to have any validity. In purchasing from companies offering both stainless and chrome-moly I bought half in each. At the time, stainless was being hyped up in the shooting press but I wanted to leave no stone unturned. This ended up being a good thing.

Upon receipt, I broke the barrels in as described in "Gas Gun Barrel Break-In" (October 2014), then built a temporary gun using the same A2 upper, match bolt carrier, and front sight housing and gas tube. The barrels were threaded for a flash suppressor and timed to 6 o'clock with three footpounds of torque. Torque on the barrel nut was set at 47 ft-lbs. and all the guns were tested in a machine rest with ten-shot groups with the same three lots of ammo. In addition to keeping the targets, I entered the data in an Excel spread sheet that automatically summed and averaged the group sizes for each ammo lot. That made it effortless to see if a given barrel was shooting average, tighter, or larger compared to other barrel brands. The same lower receiver was used with a fresh, tight-fitting Accu-Wedge in place. No test firing was conducted if there was wind. All barrels had Wylde chambers.

In trying to test all of the custom barrels on the market, it took about a decade to complete this study. This wasn't due to the testing time (although there was no small amount of work as you can easily imagine) but due to budget. Compared to the big active duty shooting teams, the Army Reserve is always the poor kid on the block. If I had the budget, I could have purchased hundreds of gun barrels and completed the entire study in a year or two. Instead, I bought barrels in the appropriate numbers to replace shot out ones as they cycled into my shop. There wasn't one added penny to the cost of the study as I used the tested barrels to replace shot out ones that would have to be replaced regardless. I simply kept meticulous records during the entire period and analyzed at the end.

I still use this same basic technique to break in and pre-test the barrels I offer for sale today. I run a shop at Camp Perry each year (Building 910-A on Commercial Row) during the CMP National Service Rifle Championships and have a table full of barrels with a test data and targets fired on the machine rest for every one. My customers can go through my book and pick their barrel. The price includes installation and load work up. I test my complete uppers the same way and includes a box of long range ammunition with 80 or 90 grain bullets tuned to the barrel. This takes the guess work out of the purchasing equation that others in the business don't offer.


Some barrel companies also attempt to "grade" their barrels but they do so based on techniques such as air gauging, not actual test firing in a machine rest. I am not saying that gauging won't help predict a good barrel but, like peering in a bore scope until you're bleary eyed, there is no substitute for actual range fire testing. I believe I am the only custom builder in the country offering this service. I read advertisements of "guaranteed" grandiose accuracy claims but test targets backing this up are nowhere to be found. When impartial testers shoot many of these guns, they often report disappointment--unless it's a gunwriter that never seems to shoot a group bigger than one MoA. I have machine rest tested many hundreds of barrels and uppers and know those shooting the one MoA and above far outnumber those that are under--at least when kept honest and using more statistically-valid ten-round groups. I completely discount three-round groups and hold five-round groups as highly suspect. A tester discounting fliers from the test forget these will also happen during real shooting. A tight, 1/2 MoA eight-round with two fliers that take it out to well over a minute is not an honest sub-minute group!

"Good Enough" Accuracy

In National Match Course competition, the Army Marksmanship Unit is the force to be reckoned with. They have a record of consistent wins like no other military or civilian shooting team on the circuit. When I was with the Reserve Team, the AMU had a contractor whose job was to conduct machine rest testing. I got to know him as he was a fellow Viet Nam vet. I asked him what their acceptance criteria for NMC AR-15 accuracy was and he said a gun shooting one MoA was passed. Given the bold accuracy claims of some civilian builders, the AMU's requirement seems modest. However, as discussed, consider how such testing is conducted.

NMC competition targets have ten rings a full 2 MoA in size. An accomplished marksman with an honest one MoA rifle leaves a full minute of shooting error for perfect scores. The AMU trains five days a week leading up to competitions and their philosophy is to provide good guns and rely on superior application of marksmanship skills in order to win. It is certainly working for them. It is fair to guess many of their ARs are capable of sub-minute groups. As a civilian gunsmith, your customers likely don't have five days a week to shoot, so it behooves us to build the most accurate guns we can.

Analyzing The Results

In The Complete Guide To AR-15 Accuracy, Derrick Martin emphasizes there are many good barrel makers in the U.S., but only if properly installed. After analyzing the voluminous data from my barrel study, I found there are barrels out there not delivering accuracy performance that the factory built into them because of three culprits.

The first is the gunsmith. One barrel installation problem is failing to stabilize the barrel extension in the upper receiver, as I discuss in "The Relationship Of Barrel Extension Diameter To Accuracy In The AR-15" (March and April 2013.) Properly done, this can reduce group sizes by about a third. I also recommend using true match bolt carriers. As reported in "AR-15 Upper Quick Fixes: Match Bolt Carriers" (May 2014) this shows an average improvement in group size of 8.8% from the match carriers with an additional 14% group shrinkage when anti-tilt pads are incorporated.

A second gunsmith failure is not properly aligning the gas tube with the bolt carrier key, discussed in "Gas Tube Alignment" (March 2014.) Selecting a chamber that jumps magazine length ammo excessively is another.

Drilling the gas port through a land is unavoidable in six-groove barrels and quite likely with five. Three or four grooves provide wide-enough grooves to accommodate the width of a gas port. The person drilling the gas port has to properly locate it and not all gunsmiths can. When buying an AR-15 barrel, choose appropriately and get a guarantee that the gas port will be located in a groove. While it may not degrade long term accuracy, it makes break in very difficult.

The second primary culprit is inferior ammo. Very few lots of 62 grain military ammo (M855, SS-109, etc.) shoot worth a darn. It has been said what's found on the commercial market consists of rejected lots that failed to pass loose military standards. No maker can deliver barrels that will compensate for such inherent poor accuracy.

The bullets in most factory and handloaded ammo don't line up straight with the center axis of the casing, causing them to enter the back of the barrel crooked and be deformed. This can be exacerbated if the gunsmith selects a chamber reamer that has a long leade and throat, jumping the bullets before contacting the lands. To realize accuracy potential, the shooter must either cull ammo with excessive run out or straighten it using a proper cartridge straightening tool. Likewise, don't "soft seat" ammunition with boat tails (seating the bullets a bit long) as it results in a "hard seat" and leads to pressure problems. Details are in "Precision AR-15 Ammunition" (April 2016.)

The final culprit in barrels not shooting to their potential is the shooter. The first, likely problem is a failure to consistently apply proper marksmanship fundamentals. Members of my team were some of the finest marksmen in the country and included many High Master classifications along with a number of national champions and a few national record holders. Despite this very high, proven skill, I found they often shot groups about double that of my machine rest. So, if actual champions aren't perfect, guess where that puts the rest of us mere mortals who are even more fallible in our skills? Learning how to properly apply marksmanship skills takes years.

Easier fixes include implementing simple solutions like the Accu-Wedge and guiding long range single shot cartridges into a uniform position in the chamber each time. Of course, the shooter has to learn and bother to use such fixes.

The final operator failure is in cleaning. This includes not cleaning the bore often enough or getting all the fouling out. The chamber is an important part of the barrel. Failure to consistently position the cartridge in the chamber will rob an otherwise accurate barrel of its potential. Clean every time you shoot and use a chamber brush.

Damaging the bore during rough cleaning is another problem. Tight metal bore guides are helpful but not foolproof. Rifling is about the thickness of a sheet of paper and are easily damaged. I have a Bartlein gain twist demo barrel split lengthwise that will make a believer out of you in a hurry. Likewise, a failure to properly break in the barrel may result in significant damage to the barrel.

Keep the bolt carrier assembly cleaned and lubed or it creates nonuniform lock ups, different positionings of the cartridge in the chamber, and unequal pressures on the cartridge case head by the bolt face, ejector, and extractor. Shooter should lube the carrier assembly after cleaning and during firing.

Store the firearm properly between range sessions. Regardless of barrel steel, burnish corrosion preventative like WD-40 or Boeshield T-9 into the pores of the bore, with heavy shots in the chamber and muzzle crown to prevent accuracy-destroying rust.

I cut average group sizes of Team uppers in half by using simple techniques like this. With exceptions like electropolishing and fire lapping, everything I did simply harvested the accuracy potential inherent in the barrel. I believe about half the potential accuracy of most AR barrels is masked by haphazard assembly, bad ammo, and shooter errors. Unfortunately, barrel makers often get the bad rap.

by Joe Carlos
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Title Annotation:TECH TOPICS
Author:Carlos, Joe
Publication:American Gunsmith
Date:Jul 17, 2017
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