Barrels For Custom AR-15s, Part 2

Coupling proper assembly techniques and a scientific, unbiased analysis leveled the field in my barrel accuracy study. My analysis found almost every custom barrel manufacturer makes a really good barrel, some of the time and at widely varying rates. Some barrel companies only produce about one really good barrel in ten while others go as high as eight for nine.

That is a huge quality control spread and it behooves custom builders to hedge their bets by purchasing from those two makers on the high end while avoiding those on the lower end, if accuracy is a prime consideration. Know Your Customer That last qualifier was deliberate. My guns are built for those tiny few AR Accurate information on barrel quality? Probably not so much… shooters trying to win High Power competitions, a tiny niche market.

I have to constantly remind myself that for the much larger AR market, match-winning accuracy may not be the prime consideration for barrel choice. Cost is a primary consideration. Those wearing a shop apron have to live within some budget constraints. When my sales are down and I go to the supermarket with only a few dollars, I have to choose between buying ice cream for Joe or cat food. Sucks to be Kitty on those days! Just kidding.

More seriously, when a potential customer approaches me at my Camp Perry store or elsewhere, eyeballing the expensive Bartlein gain twist barrels and quipping he can buy two barrels elsewhere for the same price, he is revealing that cost is more important to him than accuracy. For customers on a budget, all four of the big AR factories so frequently demonized by the popular media offer such products. Some of these barrels come with grandiose accuracy claims that I never seen met.

Others talk about triple lapping, cryo treatments, and other "features" that are not accurate by my standards. And they often shoot fliers. Despite claims of in-house manufacture by the Big Four, most barrels are originate in Connecticut with a button rifled barrel maker specializing in quantity at reasonable prices. This maker doesn’t have a reputation for accurate barrels and so their origin is deliberately left out.

Maybe some AR-15s are assembled with in-house barrels, but they’re more likely using outsourced blanks. You can often order such barrels in either steel type, preor post-ban, in a variety of lengths and contours, and a narrow choice of twist rates. These are usually six-groove barrels and the lands are cut or nicked by the gas port. A number of my customers have reported these uppers or barrels shoot big groups and they’re interested in improving them.

Unfortunately, I can’t make a silk purse out of a sow’s ear but I can improve matters. If I can schedule the work and conditions agreeable to the customer, I can do a better job with their ammo so I ask for about 100 rounds. After cleaning, I shoot machine rest groups with their ammo and from a known lot to compare. Both groups are normally well over Mo A and I save them. Most Big Four ARs use fatter 1 3/8" float tubes and contact the gas tube hard, throwing the alignment out of wack and causing big groups.

I fix that as described in "Gas Tube Alignment" (March 2014.) Then I stabilize the barrel extension in the upper receiver and remove the hightorque, accuracy-robbing flash suppressor and replace the crush washer with normal peel washers timed at about 3 ft-lbs. of torque and lots of red Loctite. Next step is tuning the barrel harmonics ("AR-15 Barrel Harmonics", October 2016) and working out along range load.

I include the final targets along with a sample box of the tuned load so the customer can see for himself how much improvement has been made. I have never had a customer refuse

to pay the bill or say that he can’t notice an improvement. Most of these guns end up around Mo A after treatment and occasionally better. I have never gotten true 1/2 to 5/8 Mo A performance from low-bid barrels and don’t expect to. Added up, customers may still see some savings with low-bid barrels, even after paying me for improvements, but not as much as they thought. Now, low-bid barrels have their place.

Anew shooter in most disciplines will take several years to build skills needed to shoot top scores with any barrel. Saving some money on the first barrel hopefully leaves enough to buy ammo to train with. Perhaps by the time that first barrel needs replacing he’ll be able to benefit from a higher priced alternative. Also, not all shooting disciplines require the tack-driving accuracy of National Match Course guns so lower priced barrels may be good enough. Most NMC competitors hedge their bets with better barrels.

Occasionally, one will try to scrimp and get lucky. Remember, almost every custom barrel manufacturer in the U. S. makes a really good barrel, sometimes, and occasionally one of those lucky low-bid barrels ends up with atop shooter. Another factor is longevity. Consider a low-bid barrel costing half as much but wearing out with a third of the round count. While barrel wear is extremely variable and can’t be accurately predicted, it’s more than just a function of round count.

Bore cleaning habits can equal or trump round count. I’ve replaced as many barrels due to neglect as from firing. Cleaning is so important and people vary so widely in cleaning practices that it’s difficult to set up a proper study to quantify wear out. As a Team armorer, I had the opportunity to make many observations on this. Understand such observations are somewhat subjective, so take this for it’s worth.

Concerning stainless or chromemoly, famed barrel maker Boots Obermeyer has said that with .223 Remington shooting the kinds of bullets and powders available at the time, he felt stainless would erode less rough than chrome-moly. Note, he did not say they would wear differently regarding throat erosion, just commenting on the difference in roughness. More importantly, he also did not say chrome-moly roughness would impact performance.

I believe Boots also had this "roughness of erosion" conversation with other shooters and some of them grew up to be gun journalists as I’ve seen this repeated in print a number of times. Of course, these accounts connect dots Boots didn’t intend and others have drawn conclusions without adequate testing. I’ve been watching this for a quarter of a century and what I’ve seen in the borescope backs up what Boots told me. Chrome-moly barrels do erode a little rougher than stainless.

However, outside of the cosmetic, there is no performance difference I’ve measured. Suppose I fielded two Brand Kbarrels, one stainless and the other chromemoly, and let’s say the C. M. shot tighter groups when new. If the barrels cycled back through my shop later, given equal treatments I’d normally find the C. M. barrel still out shooting the SS. Groups sizes may have increased but the C. M. barrel would still be tighter by about the same margin.

After witnessing this so many times, longevity isn’t better with stainless. While stainless does clean up easier, it has proven more susceptible to cleaning damage. Concerning cut and button rifling, makers of each insist theirs are better. Cut rifling barrel makers say their steel is better and button rifling process necessitates softer, lower-grade steel. The button rifler disagrees. My observations are cut rifling usually lasts longer with higher round counts.

In testing electropolishing and fire lapping, Stoney Point throat readings revealed button rifled throats consistently advance two to four times as far from the lapping process as cut rifled bores. I am not claiming forward erosion at the throat is the same from fire lapping as normal shooting due to the abrasive coating, but the increased wear happens. Draw your own conclusions. Propellant selection affects longevity as powders burn at different temperatures.

In testing 90 grain bullets in button-rifled chrome-moly barrels I received a copy of a private study listing most of the common powders and their burn temperatures. I was trying some so called "high energy" imports and the manufacturer claimed these yielded higher velocities at lower pressures. Lacking expensive chamber pressure measuring equipment, I just use primer condition and retention characteristics. I didn’t notice pressure differences or higher velocities with these powders.

What I did notice was fatter groups in the machine rest and higher velocity spreads on the chronograph between the slowest and fastest rounds. I fielded some guns with buttonrifled barrels using the imported

powder with about 500 total round counts and they were coming back in as being shot out. Throats measured excessively long for such modest use and bore scoping revealed extreme fire cracking running as much as six inches down the bore. The barrels were toast. I switched to cut-rifled barrels and the erosion and fire cracking backed way down to almost normal. Since the high energy powders were not performing all that well, I dropped them in favor of domestic powders.

Looking up the burning temperatures of these imports, they were hotter than other powders in the same general loading and velocity range. It appears using hot burning powder can damage bores and some button-rifled barrels are more susceptible to this damage than cut rifled barrels. It’s been found that ball powder burns cooler than some stick powders and that using them should improve barrel life. I have never seen any actual tests to verify this, however.

Looking up the burning temperatures of several common ball powders reveals they do burn cooler. Given what I observed with the effects of hot burning powder, I’ll let you decide if this will help. Barrels with slow twists seem to last longer than fast twist barrels. I have had AR barrels in 1:12, 1:13, and 1:14 twist rates and some of them went to five figures of estimated round counts before giving up.

Slow twist barrels are cooler to the touch with an equal number of shots fired as the bullet encounters less resistance to rotation and is out of the throat sooner, giving the hot, erosive gases less time to attack the back of the barrel. Gain twist barrels beginning with a slow twist and incrementally increasing toward the muzzle should last longer than barrels with uniform fast twists. In .223 Remington, barrels with taller 0.218" lands last longer than barrels with normal 0.219" lands.

Krieger makes all their barrels with 0.218 lands and Bartlein will give you which ever option you choose. I strongly recommend 0.218 for both longevity and accuracy. Norm Brux normally uses the tall option on his narrow-land barrels but reverts to the 0.219 on normal barrels. Barrels with long leade chambers and throat combinations shoot bigger groups with magazine length ammo at birth and wear out significantly earlier than barrels with shorter chambers.

I recommend no chamber longer than a Wylde (measuring 2.475" overall) with an 80 grain Sierra Match King bullet. Barrels with 5R rifling or narrow land options shoot fine and seem to last as long as any other barrel. Both are very susceptible to damage by improper cleaning because they are narrow up on the top surface where the cleaning rod can rub against them.

The 5R land is just as wide as any other land down at the bottom but the land is roughly shaped like a trapezoid and is more narrow at the top where the rod will be rubbing against it. Just keep this in the back of your mind in case you are selecting a barrel for a customer who is known for rough cleaning practices.

Pressure Unfortunately, a few shooters feel loading ammo too hot somehow buys additional "wind proofing" but the ballistic reality is an extra 30 to 50 feet per second provides minuscule wind bucking capability. Smarter shooters choose a higher ballistic coefficient bullet instead. However, at 1,000 yards enough velocity is needed to remain supersonic (above 1,100 fps) to the target as dropping below the sound barrier causes bullet instability.

We can deal with this pressure by choosing the right barrel options and/or by increasing dwell time (how long the bolt remains locked up.) Bolt carrier weights help a little. Superior Shooting Systems has a shotshell-sized weight worth about 0.3 grains of additional powder and 30 fps. Note, carrier weights in rapid fire events can cause malfunctions. If you choose to leave them in for all shooting, follow the included instructions on this.

This includes slightly shortening the back of the buffer, appropriate load work ups with the weight in place, and rezeroing. Another way to increase dwell time is drilling the gas port two inches forward of normal and using a longer gas tube, such as from White Oak. This is not an option for Service Rifles but is for Match

Rifles. Very Low Drag bullets have higher ballistic coefficients and can be started at slightly lower velocities to retain more speed at 600 and 1,000 yards. VLD bullets area little "pointier" and their bearing surface is frequently shorter they often pressure up less.

VLD bullets are normally loaded longer than the chamber so the bullet jams into the throat a little (about 0.000 to 0.010".) Each gun has its own preferred amount of bullet jam and this has to be worked out by the shooter and maintained with a process called "chasing the throat." Note, jamming bullets into the throat can raise pressures so perform load work ups gradually. Certain barrel characteristics lower pressures.

Chambers with a combination of along leade and throat permit long range bullets to be seated out further, tending to lower chamber pressure and allowing more propellant and higher velocity. If such a gun is to be used with magazine length ammo, along chamber is a poor compromise as jumping bullets yields accuracy degradation. I only recommend a chamber longer than a Wylde for use in dedicated 1,000 yard guns, typically a Holliger chamber for 90s with a reamer having a tighter neck.

Tall 0.218" lands make for more pressure. They also make for more accuracy with every bullet I have tested in the AR-15. The tall land may require a 1/2 grain reduction in powder charge. I recommend exploring every other low-pressure option before giving up the tall land! The standard groove in .223 Remington is 0.2240", about the same as the diameter of the bullets by design.

When I first began experimenting with first generation 90 grain Sierra Match King bullets in 2006 my Krieger barrels caused the then-thin jackets to separate from the cores. I sat down with Krieger’s Plant Manager and we discussed bore options to remedy this. His idea was cutting grooves an additional half-thousandth to 0.2245" as such a subtle change wouldn’t impact accuracy. These deeper grooves did improve jacket retention but didn’t completely cure the problem.

Group size tests with magazine length and long range ammunition proved no accuracy degradation and the incidence of fliers reduced. As an added bonus, pressures went down as the deeper grooves to lower pressure to compensate for tall lands. The 0.218 x 0.2245" Kriegers pretty much mirror the industry standard of 0.219 x 0.2240" the Krieger configuration was noticeably more accurate. Bartlein also provides this bore configuration and I use it with all my AR barrels. The land-to-groove ratio influences pressure.

As a general rule, grooves are wider than lands. Each barrel maker is free to make his lands and grooves as wide as personal preferences and tooling allow. Some barrel makers allocate 40% of the area to the lands and the remaining 60% to grooves. Another common configuration is 1/3 to 2/3, making the land half as wide as the groove. Another maker uses a 30% to 70% ratio and "narrow land" configurations go all the way to 20%:80% with a groove four times as wide as the land.

Given a normal 0.219" land and 0.2240" groove, the narrow land option pressures significantly less, allowing more powder and higher velocities with moderate pressures. The type of rifling also influences pressures. Polygonal rifling is offered by some button rifling manufacturers in the U. S. and has a less pronounced transition between lands and grooves than conventional rifling.

Barrel makers using the polygonal rifling claim it stresses bullets less and in tests to overcome bullet blow ups I saw evidence of this claim when Pac-Nor expanded their 5P line to include the 6.5 twist. Polygonal rifling has a reputation for causing more pressure and I’ve seen evidence of that with 80 grain bullets in 1:8 twist barrels. The Reserve Team had to cut loads between 0.3-0.5 grains to hold primers with these. I generally discourage polygonal rifling in .223 Remington for dedicated 1,000 yard guns.

The 5R rifling pattern (five lands, five grooves) made famous by Boots Obermeyer is more pressure friendly. The lands have a trapezoidal shape more narrow on the top. Bartlein offers their barrels with a 30% land to 70% groove ratio in both four groove and 5R. On paper, loads should pressure equally but I’ve found they don’t. 5R barrels are good for about 0.3- 0.5 grains more powder than four groove barrels. There are two possible explanations.

Since 5R lands are more narrow on top, the total surface area of the land is slightly less than with more rectangular shapes. Less surface area and less drag lowers pressure. All barrels with even lands line up directly opposite each other and uneven numbered lands (like 5R) staggers them and reduces constriction. Regardless of cause, 5R pressures less and is an optimal choice for 1,000 yards. I’m also getting stellar accuracy from the 5Rs, which is key to long range.

Five barrel makers I know of offer the 5R pattern, though Krieger

doesn’t have it in .22 centerfire. Four companies that do are Rock Creek, Satern, and Bartlein in single-point cut rifling and Broughton in button rifling (they call it 5C.) Another pressure-friendly configuration is gain twist, which starts spinning the bullet slow in front of the chamber and incrementally increases the twist rate toward the muzzle. This reduces overall pressure and the twist rate at the muzzle is what counts for stability.

Uniform twists are more convenient for barrel makers but a disadvantage to pressure and possibly accuracy. Smith & Wesson uses gain twist in certain heavy-caliber hunting revolvers and believes a bullet launched into a fast twist barrel skids a short distance over the rifling before the lands engrave enough to start rotation. This skidding deforms bullets and negatively impacts accuracy.

Even if you don’t subscribe to S&W’s theory, Harry Pope and his contemporaries realized over a century ago that slow initial twist rate contributes to longer barrel life, easier cleaning, less rotational torque, and cooler operation. The downside is increased barrel cost due to the greater machining difficulty. Shooting Military Ammo Military full metal jacket ball ammunition doesn’t have a good reputation for accuracy in six groove barrels and some of this reputation is deserved.

Even though the M16A2 and later were intended for 62 grain M855/SS-109 ammunition, team shooters found older bullets shot better with less fliers. Derrick Martin with the National Guard Team and I both experimented with barrels to optimize the FMJ military rounds. It was know with the M14 that .30 caliber barrels with odd numbers of lands shot FMJ bullets better so I tried five-groove barrels in 5.56mm caliber while Derrick was trying three grooves.

Derrick was an accomplished M14 shooter and may also have been employing lessons learned with the Brown Gun. Both of us documented better accuracy with odd-numbered lands. For three groove barrels, look at Lilja and Pac- Nor. For five groove barrels in .22 centerfire look at Bartlein, Rock Creek, Satern, and Broughton. We also independently found the NATO chamber was way too long in the throat for accuracy. I recommend using nothing longer than a Wylde chamber for shooting military ball ammo for top accuracy.

Twist Rate Football players learned long ago imparting spin to the ball makes it travel more true. Bullets do also and that is why ages ago makers began to rifle bores. Bullets require different rates of spin, mostly set by their length, with longer bullets needing more. We annotate this spin rate is by how many inches a bullet travels in the barrel while making one complete 360 degree rotation. .22 LR normally spins their short bullets one full rotation for every 16 inches, written 1:16.

Centerfire American Gunsmith Reader Services 1.

rifles usually have twist rates from 1:14 to 1:6. Each bullet has a twist rate that optimally stabilizes it. If your customer is going to only shoot one bullet all the time, it’s easy to determine optimum twist rate. Most bullet manufacturers publish recommended twist rates. National Match Course competitors shoot 69-77 grain bullets at 200 and 300 yards and longer 80-90 grain bullets at 600 and 1,000 yards. In such cases, twist rate needs to be set for the longest (heaviest) bullet.

A few gunwriters who likely have failed to perform adequate due diligence claim it’s OK to over spin bullets. In fact, they’ve coined the deceptive "over stabilizing" which almost sounds like "too much ice cream." Unfortunately, over spinning bullets is not a good thing and doing so likely compromises accuracy. No bullet is perfect and over spinning exacerbate any problems, creating fat groups and fliers. Faster twist barrels also heat up, pressure, and foul more. Don’t over spin your bullets!

Stoner designed the AR-15 with a 1:14 20" barrel for 55 grain bullets. This works fine and I have a 1:14 twist barrel that shoots 55 grain bullets at near Mo A. The military changed to 1:12 and I’ve owned 1:12 and 1:13 barrels that shot 55s fine. With the A2 the military went to a 1:7 six-groove barrel for the longer 62s. Green tip M855 also has a steel penetrator and some say keeping that centered is difficult, creating inaccuracy. Regardless, 62s usually shoot horribly! They’d stabilize just fine in 1:9.

The faster 1:7 was chosen to stabilize longer tracer rounds that are inherently inaccurate anyway. The combination of over spinning 62s coupled with six-groove barrels and the inherent inaccuracy of the ammo results in difficulty hitting targets at 300 meters, sometimes even closer. If you are building a rifle for someone with a pile of 62 grain green tip I recommend 1:10 or 1:9 with three or five grooves. A rifle shooting 55 grain FMJs does best with 1:14-1:12 with three or five grooves. Wylde chambers in both.

A NMC gun shooting 77s and 80s needs 1:8-1:7.7. Unless building a dedicated 1,000 yard gun, I see no reason to go all the way to 1:7 twist. The Reserves shot 1:8 barrels with 80 grain boat tails and VLD just fine even out to 1,000 yards. The difference in RPM between an 1:8 and 1:7 is 35,357. Over spinning bullets by that much will result in degraded performance. To optimize 90 grain bullets, use 1:6.5, ideally with again twist. Don’t Overlook Chrome-Moly!

As with the errors of jumping bullets in a too-long throat and over spinning bullets, another piece of misinformation regards barrel steel and the misbelief that stainless steel is always best. Stainless was hyped endlessly during the my decade-long barrel study. I grant that stainless is more corrosion resistant but I couldn’t find any real studies concerning accuracy potential.

I kept records on hundreds of barrels made with stainless and chromemoly and in every brand of barrel offering both types, chrome-moly shot tighter groups with less fliers. 50% of all C. M. barrels I tested came out shooting better than average while only 41% of stainless could make the same claim. 28% of stainless barrels shot fatter than average groups while only 15% of C. M. barrels did so. And when all the groups were compared C. M. shot 9.6% tighter than stainless.

I went into the test figuring that stainless would top chrome-moly and was surprised early on to actually be able to see C. M. performing better. I don’t know why this is, but considering the volume of data I amassed and records I kept I am certain of the final results. Two Best Barrels In my study, two barrel companies consistently made the most accurate barrels. Some companies dropped from consideration, such as those only making stainless options and low-bid makers offering cheap blanks of questionable steel.

I was lucky to get one or two barrels for every ten from such manufacturers that shot to my standards! All the companies using button rifling eventually dropped off. Lilja hung on the hardest and I like their threegroove design and their .22 LR barrel is second only to Krieger. The last two barrel companies left standing were Krieger and Bartlein. When I arrived at my final conclusions I asked what these two outfits had in common. Both use the single-point cut rifling method, good steel, and tall 0.218" lands.

I am getting good wear from both. Quality of tooling and a commitment to excellence are also prime factors. I wish I could have included Obermeyer barrels in my study because I’ve had great success with them in M14s and AR-15s, but during the time of my testing Boots was tied up in a DOD contract making barrels for rotary cannons and wasn’t doing much on the civilian side and I was unable to get barrels from him.

I build guns for National Match Course competition shooting 90 grain bullets and have achieved 3/8" ten-shot groups. That is the kind of accuracy performance you can obtain with a quality barrel, a 90 grain Berger boat tail bullet set to the sweet spot, and proper gun building techniques. I used a chromemoly Bartlein gain twist barrel with 0.218" lands, 0.2245" grooves in a 5R rifling pattern. The 20" barrel had a Wylde chamber with 1:13 twist at the throat and 1:6.5 at the muzzle.

These are the best barrels I have ever shot and my acceptance rate with them is eight out of every nine, the highest in my study. I hope the tips passed along in this article help you to build guns as accurate by making wise barrel choices! AG