Building The 90 Grain AR-15, Part Two

Bullet, barrel, bedding. Back in the M14 days we figured that if you got these three things right you’d have a tack driver. The AR-15 has eliminated the bedding issue (kinda/sorta) so we can concentrate on the remaining two. In this installment we will talk about barrels and next time will cover bullets and other 90 grain loadings issues. Last time we said that you will need a barrel with a 1:6.5" twist to shoot 90s optimally.

There are barrels in 1:6 twist and 1:7 twist that are just on either side of that which should also shoot 90s. Of the three manufacturers of 90 grain bullets, Sierra and JLK recommend a 6.5 twist. Berger says a 1:7 twist will work with their bullets. I have tried a couple of different brands of 7 twist barrels with the Bergers and never had much luck. While the bullets stabilized and went in straight, groups were just too big for my liking. These experiments were tried with 20" service rifle barrels.

Perhaps in a 26" match rifle barrel where a person could get a more velocity (about 100 fps) the 7 twist would work. I have also tried 1:6 twist 20" barrels with the 90s. The 6 twist worked better than I expected and a whole lot better than 7 twist. In fact, one of them is the best barrel I have ever tested in any twist rate and any bullet. There are disadvantages to going to a 6 twist, however. Barrel heating, fouling and pressure will worse.

Let’s face it, it takes a lot to overcome the inertia of a 90 grain bullet in .223/5.56mm cartridges in the first place. Trying to get that bullet not only moving down the bore but rotating once every 6 or 6.5 inches is quite a chore. A 6 twist barrel only makes pressures worse and with no pay off with long 90 grain bullets, so you can imagine how much this over spins 77 grainers on the short lines.

Sometimes I hear the phrase "over stabilizing" used in place of the proper term, "over spinning." Over stabilized almost sounds like "too much ice cream" but a bullet is stabilized at a certain twist rate and increasing beyond that point won’t net more accuracy. Over spinning too-thin jacketed bullets can result in mid air blow ups before reaching the target. Before we talk about the various barrel options we need to discuss the pros and cons of what is offered.

Obviously not all barrel companies agree or everybody would make their barrels alike. Not all gun writers and shooters agree either. I can only relate what I have seen in the past eight years of working nearly every day with 90 grain bullets and the barrels that are available to shoot them. If you are shooting other bullets my observations may not apply. I have tested about 100 1:6, 6.5 and 7 twist barrels to date in both 20" Service Rifle and 26" match rifle lengths.

There are two general types of barrel steel, stainless and chrome molly. Within those broad types there are different alloys and barrel manufacturers are free to choose which they use. Price is no doubt a factor in their decision making. Each alloy will machine and wear differently. When I first started working with the 90s I fielded several, mostly chrome molly, button rifled barrels that were driving tacks. Loads used high energy imported powders.

Within about 500 rounds they all started tearing jackets off Sierra 90 grain bullets and causing them to explode. My first thought was that the throats had eroded and the bullets were jumping too far. The bullets that were blowing up were boat tails, not VLDs, however, and I initially thought they should be jumped as the throats grew longer with use. When I called the guns back in and bore scoped them the throats and the whole back sections of the barrels were rough as a cob.

That roughness was tearing up the bullet jackets as they passed through. Remarkably, some of those barrels were still shooting thicker jacketed 77s and 80s fairly well. That experience caused me to recalla conversation that I had with Boots Obermeyer nearly 20 years ago. We were talking about the .223 cartridge, the powders used in it and the pressures they develop. Boots told me that considering all these factors he felt stainless barrels would generally erode smoother in the AR-15, but not necessarily less.

As I was bore scoping those rough barrels I also remembered hearing anecdotal reports that the imported high energy powders burn at a higher temperature than conventional powders and this might result in rougher throat erosion. I sent an email to the technical representative of the powder company in question asking if he could either confirm or deny this claim and if there was validity to the rumor, could he recommend another powder in their line

that might be friendlier to my barrels. I received no reply. I followed with a second email a year later which also met with silence. I then asked a number of gun barrel manufacturers and gunsmiths if they had any experience in this regard. Some said that they had heard the same rumors and that it seemed to make some sense but none had performed any experiments to scientifically prove or disprove the idea.

Finally, I got hold of a private study that had been conducted that confirmed the rumors about higher temperatures associated with high energy powders. I can’t say if the higher burning temperatures were the only factor in the rough erosion. Powder chemistry is an esoteric topic that I don’t want to get into here but suffice to say that some powders are believed to leave behind a residue that actually acts somewhat as a lubricant for the passage of the next bullet.

Based on that early experience I made two changes, one of which I still stand by. I abandoned the use of high energy powders entirely in my chrome molly barrels. Since I made that decision the life of my chrome molly barrels has doubled to quadrupled. Bore scoping chrome molly barrels confirms that less rough erosion occurs. For about a year I bought nothing but stainless barrels in 6.5 twist. The longevity of them was good but I wasn’t happy with the accuracy.

There can be machining differences between the two steels and those differences can affect accuracy. Those machining differences can also manifest themselves in how the barrels treat the bullet jackets that pass through them and I was having a lot higher incidence of 90 grain bullet failures when I was buying stainless. I guess one of my shooters summed it up best, saying if a barrel isn’t shooting top notch, who wants it to last along time?

The only stainless barrel that I am currently using with 90s is the very good Brux 6.6 twist narrow land. Before I give you the contact information to purchase a barrel we have to briefly discuss numbers of lands, rifling patterns, and chamber options. There is a general theory that, all other things being equal, a barrel with a low number of grooves will stress a bullet less than one with a high number of grooves. Therefore, a three groove barrel should stress bullet jackets less than a six groove.

The theory is extended to say that barrels with fewer grooves will also foul less. Again, one brand of 90s has a reputation for blowing up so we want to reduce stress on their jackets. Polygonal (available from Pac-Nor with five grooves, designated 5P) and Russian canted land configurations (available from Rock, Bartlein, and Satern with five grooves, designated 5R) are supposed to stress jackets less than conventional rifling.

And to top it all off, odd numbers of lands (three or five) are thought to stress bullets less than even numbers. The theory is that with even land numbers the lands will be directly across from each other. By pressing in on the jacket lined up this way there will be more stress imparted. Odd numbered lands will be staggered and never line up directly across from each other. My tests with 90s show that there is some merit to all these theories and I would take them into consideration when choosing a barrel.

You can get away with abusing 77 and 80 grain bullets to a far greater degree than with some of the 90 grain choices. I recommend building in all the advantage you can get by making wise barrel selections. Quality of workmanship can’t be overlooked. You can employ all the theories in the world but if the barrel maker buys bad steel or rushes the job the end product won’t shoot well.

Chambers This one is easy if you are building a gun for 200, 300 and 600 yard shooting where magazine-length 77s are used at the short lines. Wylde! I know that some civilian shooters like shorter chambers, such as available from Compass Lake, because the slightly shorter throat gives them a little greater longevity when shooting 77s and 80s, but the 90s are longer bullets and that length needs to go somewhere, preferably not buried way below the case neck.

I think that the slightly longer throat in Bill Wylde’s dimensions is a good compromise and will allow you to achieve velocities that will keep bullets supersonic to the 1000 yard line at pressures you can live with. I have learned the hard way that you need a 1 degree 15 minute leade angle on your reamer. This will ease the bullet into the barrel better than the sharper 1 degree 30 minute .223 reamers that are very common.

Some chambers even go all the way to 3 degrees, which would really eat some bullets for lunch. Be warned, I have seen all kinds reamer dimensions passed off as supposedly being Wylde. Check the blueprint and confirm that it has the shallow 1 degree 15 minute angle. If you measure a true Wylde chamber when new with an 80 grain SMK and a Stoney Point Comparator, you should get an overall length reading of 2.475".

Note, use of chambers with longer throats (overall readings of 2.50, 2.55", etc.) may be helpful in reducing chamber pressures, promoting "softer" obduration of the fragile Sierra 90s, and achieving higher velocities to support 1000 yard shooting. Longer throats will significantly degrade 77 grain performance, however. I recommend you only consider longer throats in rifles dedicated to shooting beyond 600 yards and make sure they have the 1 degree 15 minute leade angle of the Wylde.

John Holliger at White Oak offers such a chamber and I recommend it to anyone not shooting any mag-length bullets. Most other long throated reamers will have a more abrupt leade angle and will do more damage than good with regard to jacket retention. Also understand

the trade off in longevity of the barrel. Barrels born with longer throats shoot out sooner! Some of the barrel manufacturers I list will only furnish you with the basic rifled blank and you will need to have it turned, chambered, headspaced with the barrel extension installed and the gas port drilled. Others will do all of that for you.

If you elect to buy a blank and don’t know who to send it to for the additional work, I recommend Compass Lake Engineering (compasslake.com, Frank White has probably done several hundred barrels for me and at least 100 of them in 6.5 twist. His Wylde reamer has the correct leade angle, his prices are competitive and turnaround time is reasonable. They are able to blacken your chrome molly blank if you choose that steel.

When shipping three or four groove blanks, be sure to stress that you want the gas port drilled in a groove and that you will not accept cutting of a land with the port. Of course, drilling gas ports in any six groove .22 center fire bore will result in cutting a land, probably also in five groove .22 caliber barrels as well.

For button rifled blanks in chrome molly or stainless six groove 1:6 twist, I recommend Douglas Barrels, Inc. (douglasbarrels.net, These barrels will shoot Berger 90 grain boat tails and VLDs well but are not "Sierra proof." For stainless button rifled six groove 1:6 twist complete barrels, go with Hart Rifle Barrels (hartbarrels.com, This barrel maker is the only one I have not tried with the 90s.

I don’t know what their chamber options are but they will also sell you a blank which you can have turned and chambered elsewhere. For Pac-Nor button rifled barrels in either three groove standard or five groove polygonal chrome molly or stainless steel, contact Noveske Rifle Works (noveske.com, For one stop shopping. John Noveske will turn and chamber the Pac-Nor blank for you and he has the correct lead angle on his Wylde reamer.

Their chrome molly 5P (five grooves with polygonal rifling) and conventional three groove barrels are the most "Sierra proof" barrels I have ever tested. Accuracy with both is stellar shooting 77 and 90 grain Sierras. The Pac-Nors will also shoot the new Berger 90 grain thick jacketed boat tails but really like the Sierra 90 the best. I have not had similar luck with Pac-Nor 6.5 stainless, however. Nor have I had much luck getting any Pac-Nors to shoot VLDs.

Other people report that they have been successful with VLDs in Pac-Nors, however. John Noveske will also turn and chamber blanks provided by Douglas, Krieger, Bartlein and others if you ask him to. His work is very good. When dealing with three or four groove barrels be sure to stipulate that you expect the gas port to be drilled in a groove and that you won’t accept a barrel with a land cut by the port. Note, polygonal rifling has the reputation of pressuring up a little more than conventional rifling.

I have seen this with other barrel brands but don’t remember it striking me with the Pac-Nors. Take this into consideration when building 1000 yard rifles where it is critical to start bullets at very high velocities. For Across The Course shooting out to 600 yards, I wouldn’t worry about it. For Badger’s six groove, broach cut, 6.5 twist, chrome molly steel barrels, try Northern Competition (northerncompetition.com, Again, one stop shopping.

This is the only company that I list having finished barrels in stock ready for immediate shipment, or immediate instillation if you ship them your upper. They make Wylde chambers with the proper leade angle and stock 20" barrels in multiple configurations as well as 26" match rifle 6.5 twist barrels. All come standard with a blued finish. Isonite coating, a saltbath nitriding process applied to both the inside and outside of a barrel by MMi Trutec (parkertrutec.com), is available upon request.

I have found barrels processed with this finish to clean up easily and to be corrosion resistant, especially important if choosing chrome molly. Badger barrels are made from a good quality, special order, low sulfur C. M. steel that wears well. So far the Badgers that I have tested liked the Berger VLD bullet and was pleasantly surprised with the Sierra 90s.

Considering they have six grooves and cut rifling, which sometimes tends to be sharper than button rifling, I was fearful that the deck was stacked against the Sierras and opted not to field Badger barrels with them. Badger barrels also shoot 77s and Berger 90 grain boat tails well. Northern Competition is the only company I will let flute barrels for me because they use a slow, very low stress inducing method.

They also market and install their own National Match, double pinned, ¼x¼ minute rear sight and what I consider to be the best 1-3/8" float tube on the market. They have expander mandrels in stock to set the proper neck tension on new primed military WCC and LC brass for loading 90 grain bullets.

For four groove, single point cut, 6.5 twist blanks or completed barrels in either chrome molly or stainless, contact Krieger Barrels, Inc. (kriegerbarrels.com, Krieger is noted for tightness in their internal dimensions (0.218" lands as compared to 0.219", which is more standard in the .223 Remington) which, coupled with meticulous machining and quality barrel steel, normally results in a combination of good accuracy and longevity.

Their standard 0.218" x 0.2240" internals works well with both VLD bullets but is murder on the touchy Sierra 90s!

Several summers ago I sat down with their plant manager while at Camp Perry during CMP week and we talked at length about the problem with Krieger barrels shredding Sierra jackets. We decided that relaxing the groove diameter to 0.2245" (the standard dimension is .224") and heavily finish lapping the barrel might help the problem. It certainly did! In chrome molly it shoots very well and comes close to being "Sierra proof." I refer to this modified barrel as the USAR Pattern.

If you are ordering one and use that phrase, specify the 0.2245" groove and the fact that you want to shoot Sierra 90s, I am sure they will know which to make for you. For shooting Berger boat tails, the 0.218" land and 0.2245" groove is my choice to try to control pressures and lessen fliers. Like Pac-Nor, I see better accuracy performance from Krieger’s chrome molly than stainless.

Again, if ordering a finished barrel from them specify that you expect the gas port to be drilled in a groove and will not accept a barrel where a land is cut by the gas port. For 5R, 6.5 twist, single point cut stainless or chrome molly barrels, try Satern Custom Machining, Inc. (saternmachining.com, They will make the blank, turn and chamber it with a proper leade, headspace and furnish the barrel extension and bolt. Service rifle 20" and 26" match rifle barrels are all available.

They use a quality steel with good wear properties. If you plan to shoot the new Berger boat tails, ask for their 0.218" land and relaxed 0.2245" groove. Avoid sending their barrels out to be salt bath nitrided. They tell you right on their website not to do this!

If you or your customer insists on having one of their barrels coated, follow the instructions in my previous article on, "Retention Of AR-15 Barrel Extensions" (September 2013.) The last Satern barrels I purchased had the extensions put on with extremely light torque. Likely hand tight with red Loctite. Every one of them came right off after being nitrided. It is very embarrassing to have a barrel start to unscrew in a customer’s rifle.

For 5R or 4 groove, 6.5 twist, single point cut rifled blanks in either stainless or chrome molly, look at Bartlein Barrels, Inc. (bartleinbarrels.com, Their normal bore is a tight 0.218", like a Krieger, with a 0.224 groove. They will also give you a 0.2245" deeper groove if you ask. Call it the USAR Pattern. I would go with that 0.218" x 0.2245" option for the Berger boat tail. The deeper 0.2245" groove helps control pressure and lessen fliers.

Bartlein double laps their barrels, once before cutting the grooves and again afterward. For 5R, 6.5 twist, single point cut rifled blanks in either stainless or chrome molly, try Rock Creek Barrels, Inc. (rockcreekbarrels.com, To date I have only tried their stainless blanks and they exhibited very good wear characteristics. All three brands of 5R barrels (Satern, Rock Creek, and Bartlein) shoot JLK VLD 90s well.

I am working with Bartlein on again twist that begins with 1:13" at the chamber and doubles to the muzzle where it hits a final 1:6.5" twist. It easily controls pressures and allows hitting 2,600 fps at the muzzle while keeping primers intact. Accuracy is stellar with both 77 and 90 grain bullets. Specify the 0.218" land and deep 0.2245" groove. If you are going to shoot 1000 yard events with a Service Rifle, this in a 20" barrel is the ticket. You can also use it for ATC shooting, yielding a competitive to 1000!

Note, when ordering gain twist blanks the barrel maker needs more information than usual in order to get it right. You don’t just send them an email asking to start in front of the chamber at 1:13" twist. You have to tell them how long your chamber is (1.94" with a Wylde, including American Gunsmithing Association

throat) and how much you intend to cut off the back of the blank in the machining operation. Likewise, you don’t just tell them you want to have the final twist at the muzzle come out at 1:6.5" because you are going to cut some off in the machining process. Some of you may cut off ½" while others may cut off an inch.

If all this sounds like techno-babble or you are having trouble visualizing it, stop at my Camp Perry store front on Commercial Row (Bldg. 910-A) during CMP Service Rifle week and I’ll have a 20" AR-15 gain twist barrel split lengthwise and that will help make sense of things.

For four groove, single point cut rifled 6.6 twist barrels in stainless, try Brux Barrels (bruxbarrels.com, Their product came to me highly recommended and they will provide a complete barrel with the extension installed in either 20" service rifle or 26" match rifle lengths. Their standard land configuration (60% groove/40% land with an industry standard 0.219 bore) in a stainless barrel with four-groove, single-point cut rifling shoots well with Berger 90 grain VLDs.

I have not had the same luck with JLKs in the Brux bore and have never tried the Sierra boat tail in them. For 1000 yard use with the new Berger 90 grain boat tails, I recommend the Brux narrow land configuration American Gunsmith Mailing List Policy Like many other publishers, we make portions of our customer list available to carefully screened companies that offer products and services we believe you may enjoy.

If you do not wish to receive these offers, and/or information, please let us know by contacting us at: American Gunsmith Opt-Out Program Norwalk, CT 06854 Please include your current mailing label. (80% groove/20% land with the tighter 0.218" bore option) to help control pressure when attempting to drive the bullet to 2,600 fps, which Berger recommends for best performance.

Stainless Brux 6.6 twist narrow land and Bartlein gain twist barrels are the only 20" service rifle barrels I have been able to consistently achieve 2600 fps with the thick jacket Berger 90 grain boat tails while maintaining 100% primer retention. The narrow lands really help control chamber pressure and accuracy with both 77 and 90 grain boat tails is stellar, making it a good choice for ATC and 1000 yard events.

Bartlein’s gain twist has wider lands than the Brux and I believe it wears better, giving a higher round count before shooting out. Again, stress to them that you expect the gas port to be drilled in a groove. RKS Enterprises in Canada makes six groove gain twist stainless and chrome molly blanks. Like Bartlein, RKS will make any gain you desire. I recommend 1:13" just in front of the chamber doubling in the next 18" to 1:6.5" at the muzzle.

Ron Smith will also give you the tall 0.218" land and deep 0.2245" groove that has proven so successful to accuracy, pressure control, and reduction in fliers. To date I have only tested a limited number of their products. If you want a single point cut rifled gain twist barrel quickly, their delivery time is less than half that of Bartlein, a significantly faster service at a similar cost.

RKS does not lap their blanks, however, but their break in is not overly difficult and the appearance of their blanks in the bore scope looks smooth and very clean. In summary, if you want to shoot Sierra 90 grain boat tails I recommend the two Pac-Nors, the 3 groove or the 5P in chrome molly. They are most certainly not guaranteed to be "Sierra proof" and when throats lengthen and get rough as you jump bullets further into them, you can experience bullet failures.

I have been torture testing the Bartlein gain twist 1:13 x 1:6.5" with the old Sierra 90s and have yet to blow a bullet. Gain twist may end up becoming the solution for that fragile bullet but I want more test data before making that recommendation. For JLK VLDs the 5Rs from Rock, Satern, and Bartlein seem to be the best. Berger VLDs seem to shoot well in all but the Pac-Nors. Berger 90 grain boat tails shoot well in almost all barrels for ATC performance at speeds of 2,500 to 2,550 fps.

My top two picks for the Berger boat tail remain the "USAR Pattern" from Krieger and Bartlein. I performed a study where I compared rifles shooting 80 grain bullets to rifles with "USAR Pattern" barrels shooting 90 grain Berger boat tails and the latter shot fliers about half as often and with about half the severity. For 1000 yard events a 5.56mm needs to push a 90 grain bullet at least 2600 fps at the muzzle.

I would recommend the Brux narrow land 6.6 twist in stainless with 0.218" land and 0.2240 groove, the Bartlein or RKS gain twist 1:13 x 1:6.5" with 0.218" lands and 0.2245" grooves. Obviously, if you want just one gun that will perform from 200 to 1000 yards, these are also the barrels of choice. AG