Building The 90 Grain AR-15, Part Three

All of my 90 grain AR-15 loading data was developed in Wylde chambers, being a good compromise chamber when shooting both 77s at the 200 and 300 yard lines and 90s for 600 and 1000 yard lines. I used new military Western Cartridge Company or Lake City brass with crimped primers in all load development. Always work up gradually from well below any recommended loads, watching closely for signs of pressure.

Measure your chamber using a Stoney Point (now owned by Hornady) overall length gauge and an 80 grain Sierra Match- King bullet. Yes, I know we are shooting 90s but the standard of measurement was developed ages ago before 90 grain .22 caliber boat tail bullets were even invented. If your chamber is a true Wylde it should measure 2.475" overall, from case rim to bullet tip. Don’t worry much as long as you’re within 0.010", plus or minus, but be ready to adjust your loads if you have a much larger discrepancy.

Shorter chambers require reductions in powder charge weights. Remember, gunsmiths chambering these barrels may work on hundreds a year and reamers wear out. They may order Wylde replacement reamers but not all reamer companies deliver the exact same dimensions. I use competition bullet seating dies with micrometer adjustments so I can vary my bullet seating depth in 0.001" increments to hit the sweet spot. My initial average jump for these boat tails is about 0.004", roughly the thickness of a sheet of copy paper.

I have guns set all the way from 0.000" to 0.010". When I take Stoney Point readings I don’t shove the bullet up hard into the back of the barrel. I push it gently until it contacts and then stop. Everyone’s measurements will vary from those taken by another person. Make sure your barrel and chamber are immaculately clean before attempting to use the Stoney Point.

For 90 grain boat tails I recommend starting with my 0.004" jump and work back and forth initially in 0.002" increments until you see which way your gun wants to go. Then you can fine tune down to 0.001". Once you find your bullet seating sweet spot you can probably leave it set there for an entire shooting season. Boat tails are not like VLDs and don’t require chasing the throat.

Note, when setting jump and establishing sweet spot bullet seating lengths you will be using the actual 90 grain bullet in question, not the Overall length gauge in center is used to identify what chamber is in a gun. Headspacing attachment on bottom is used to adjust sizing dies for proper 0.003" shoulder bump. 80 grain SMK which is just used to communicate lengths with other loaders. You will need to have the comparator and appropriate bullet insert attached to the caliper to establish this.

I know this may sound a little confusing and esoteric at first. Read Glen Zediker’s Handloading for Competition. I am planning a series of articles on making ammunition in the future. Stay tuned. Brass Issues Some notes on brass, shoulder bump, concentricity, primer retention and neck tension. Brass used in my load work ups was all new WCC or LC military with crimped primers, shot once and thrown away.

If you are using used brass or brass without crimped primers, your primer retention issues will be likely more severe and you may have to reduce charges. A bolt carrier weight may help but if you are going to use one

From left, a K&M 0.2235" expander, custom mandrel by Northern Competition beside the die body from Sinclair that it fits into and Redding Type Sfull length sizing and neck sizing dies with an interchangeable bushing in the foreground. make sure it is in when working up loads and zeroing. I recommend removal of carrier weights for 77 grain rapid fire shooting as they can induce malfunctions.

I use quality Lapua brass in many cartridges and really like it, however, I avoid it in the .223 because it is thicker and heavier than the military brass. I don’t think you can get Lapua with factory crimped in primers. My experience has shown that you have to reduce powder charges about a half grain when using Lapua brass. For 90 grain slow fire ammo I run a pretty light neck tension of about 0.001" to 0.0015" and heavier neck tension, obviously, for 77 grain rapid fire ammo.

To obtain that, I run a hardened 0.2235" mandrel down the snout of the casing. Northern Competition should be able to furnish you with such a mandrel, stocking 0.224" sizes and can easily turn down to a half thousandth. You can also custom order from K&M Services To get the same kind of neck tension on a military casing that has been fired in your chamber, use a 0.247" outside neck bushing.

Neck size the casing only (no need for full length sizing for slow fire) and bump the shoulder back about 0.003" so it feeds and extracts well. Use a headspacing attachment to determine when you have the 0.003" bump right. Use a quality competition neck sizing die. My tests have shown about a 21% improvement in group size when properly outside neck turning cases. Use a hand tool and follow the manufacturer’s instructions.

When reloading neck turned cases, substitute a 0.246" neck bushing to keep the same neck tension. Cartridge concentricity is key in competitive shooting and especially important in any fast twist barrel (1:8 to 1:6.5".) I recommend never shooting any round, 77 or 90 grain, in competition that has more than 0.003" of run out. Porter Precision and Hornady both market tools to straighten out-of-round cartridges.

In order to get reliable adjustments, practice using these devices to The Sinclair gauge in center just identifies misalignment of bullet to casing. straighten rounds that gauge 0.004" or more initial run out. Powder I use Alliant Reloder 15 or Vihtavuori N140 powders in 90 grain loads for 20" service rifle barrels, having tried others in the same burning range, such as Hodgdon Varget, Accurate AA2520 and VV N540.

Such powders all pressured up about the same as RL15 and N140 but usually shot slightly fatter groups and exhibited higher maximum extreme velocity spreads, resulting in vertically strung groups, especially at 1000 yards. The Army Marksmanship Unit may have used VV N550 in their 20" barrels back in the early 2000s when they were shooting 90s, which is slower burning than the others. My experience indicates it shoots fatter groups and exhibits noticeably higher maximum extreme velocity spreads.

It may be that a 20" barrel is just too short to get such a slow burning powder to perform optimally. N550 is a fine stick powder so you can get more of it in a .223 case. Start at about 25.0 grains and cautiously work up to no more than about 26, watching pressures as you approach the higher levels. One of the few persons I know to have ever blown up an AR-15 did so with a 90 grain Sierra backed with a charge of N550 exceeding 26 grains.

If you are trying to hit 2,600 fps muzzle velocity and can’t get RL 15 or N140 to stay within pressure limits, you can

Author’s favorite powder is Vihtavuori N140 in the small container. Beware of the high energy powders on right as the author experienced early and heavy fire cracking, diminished accuracy and inconsistencies in velocity with them. probably switch to N550 and make it. The downside may be fatter groups and higher maximum extreme velocity spreads, however, each gun is different so it may be worth seeing how N550 performs in yours.

Both high energy Vihtavuori powders (N540 and N550) burn at hotter flame temperatures than most American powders. When I was using button rifled chrome-moly Pac-Nor barrels the imported powders ate them for lunch. I had any number of such barrels shoot out at 500 round counts! Bore scoping revealed heavy and deep fire cracking from the throat down the bore for about six inches, roughness that was tearing the fragile Sierra jackets to shreds. If you are going to use these powders I recommend cut rifled barrels.

Stainless barrel steel seemed to resist the roughening somewhat better. Everything in shooting is a trade off and shooting 90s is no exception. VV N140, however, will not damage barrels excessively, is very accurate and gives consistent velocities. It is my first pick for 90s.

Bullets JLK 90 grain VLDs are the original bullet from Jimmy Knox that was around for years before the Army Reserve Team discovered that 5R rifling patterns (1:6.5" twist) offered by Bartlein, Satern, and Rock would optimize the performance of this 90. When the AMU was shooting this bullet in the early to mid 2000s, the 5R hadn’t been offered in 6.5 twist yet. I am pretty sure that the AMU would have done better with the 5R barrels that are available today.

Some USAR Pattern Krieger four groove barrels (0.218" bore with 0.2245" deep grooves) will also shoot the JLKs well. I have not had much luck getting the Brux four groove barrels to shoot it, however. The Pac-Nors don’t like either VLD bullet. JLKs are now available from Swampworks Inc. (swampworks. com, and the new owner, Steve Milholland, only makes one or two runs of 90s a year so order well in advance. The JLK requires "chasing the throat" because it is a VLD.

The JLK has the highest ballistic coefficient (.580) of any 90 on the market and are probably the most costly. You will want to hit a muzzle velocity of about 2,600 fps for optimal 1000 yard performance. Try charges of 23.5-24.4 grains of either RL15 or VV N140 depending on the preferences of your specific barrel. This bullet seems to like a fairly heavy jam into the rifling. Plan on 0.005-0.010" of engagement. This seems to be a reliable bullet and I don’t know of anyone who has ever blown one up.

It will give you about 28.6% wind-proofing advantage over the 80 grain SMK. Berger (bergerbullets.com, 90 VLDs now have a thicker jacket but most of my experience with this bullet was with the old thinner jacketed version. I have had good luck getting the Berger to shoot in across section of barrels. About the only barrels that didn’t like either it (or the JLK) were the two Pac-Nor offerings. The B. C. Is a respectable .551.

Go with the same charge, velocity and throat recommendations as the JLK, though the Bergers seem to like a little less aggressive jam into the rifling. This bullet is usually available for mail order from Sinclair and Midway. The Sierra (sierrabullets.com 90 grain Boat Tail is readily available from many gun shops and mail order sources. When this bullet was introduced in 2005 many folks hoped it would replace the venerable 80 grain SMK as the mainstay in the AR-15 for long range competition.

Although Sierra cites me as providing the first creditable report of the bullet blowing up, others very quickly shared the dubious experience and the bullet got a really bad reputation on the firing line. Due to some confusion as to exactly what bullets were blowing up, the reputa-

Which bullet do you want to be shooting in rapidly changing wind conditions? tion of other 90 grain bullets became collateral damage. The B. C. of the Sierra 90 is .504 (their 80 grain Match- King is only .420) and in order to keep it reliable to 1,000 yards the factory recommends a 2,650 fps muzzle velocity, 50 fps faster than the others. I was able to get the recommended 2,650 fps and remain within safe pressure limits. Try 23.8-24.4 grains of RL15 or VV N140.

Achieving that kind of velocity in a 20" service rile barrel, however, resulted in some really rough obduration and other stresses on the bullet, and blow ups were common. I have never had an accuracy problem with this bullet, just reliability issues. The original Krieger constricted 0.218" bore with a standard .2240" groove ate Sierra 90s for lunch. I worked with the bullet and barrel makers for about two years and I came as close to getting it to work as anyone.

The Pac-Nor 5P and conventional 3 groove chrome-moly barrels, especially if electropolished by Black Star, were reasonably "Sierra friendly," but not entirely "Sierra proof." The Krieger USAR Pattern (0.218" bore with deep 0.2245" grooves), if electropolished, was probably the second friendliest barrel configuration. Electropolishing reduced constriction and smoothed out any remaining tool marks in the bore that could snag at bullets on the way by, weakening them. There was always that nagging doubt, however.

If you have ever blown up a bullet you won’t soon forget. There is enough pressure on the shooter on the line trying to deliver a good score. Adding to this the uncertainty that all twenty bullets might not reach the target is just not fair. I have spoken to folks at the Sierra factory about this bullet many times. They know how to fix it. So why haven’t they? They say that they still sell a few bullets from the last factory production run dating nearly back to the origin of the bullet in 2005.

I suppose if customers were willing to drop muzzle velocities back at least a couple of hundred feet per second and just shoot the bullet to 600 yards a person might be able to keep the jackets intact. Obviously doing so would degrade the "wind proofing" of the load a little. Most of the wind bucking ability of this cartridge comes from the high B. C. of the bullet, however. If you are thinking about using the bullet this way I recommend setting the jump to be about 0.004".

Chase the throat just like a VLD and never let bullet jump exceed 0.020". Exceeding 20/1000" of bullet jump seemed to exacerbate bullet blow ups when I was working with it. Persons wanting to shoot occasional 1000 yard matches with their 6.5 twist rifles could shoot one of the VLDs. Sierra’s second stated reason for not fixing the bullet has frequently been the limited sales. My counter argument to Sierra has always been that this is a chicken/ egg issue.

I believe that a market may still exist but the reason Sierra 90s are not selling is their reputation for blow ups. Sierra should know their market better than we do. I talked to them about the bullet again a few months ago while I was working on this series of articles. They said that the future could either see them just withdraw the bullet entirely or fix it. At the time we spoke it could go either way. Berger also makes a thick jacketed 90 grain boat tail. The B.

C. of this bullet is .512 which results in about 17% of wind proofing over an 80 grain SMK. This is the bullet I think the majority of you will be most interested in. Berger recommends a muzzle velocity of 2,600 fps to keep this bullet accurate to 1000. A few years ago Blackstar was forced to stand down their barrel electropolishing process. They used an acid and the storage and disposal of that acid came under strict control by various environmental agencies.

The cost of doing business became so restrictive that Blackstar was forced out of business. So, I decided it was also time to explore other 90 grain bullet options. I contacted Berger to see if they would be interested in producing a quality, user friendly, 90 grain boat tail. They could see that there was a noticeable void in the current market and readily agreed. Given the bad reputation in the High Power community for bullet blow ups, we agreed that a thick jacket would be a must.

About six months later, in October 2008, I received my first shipment of the new bullet. Given my previous history of bullet blow ups the first thing I did was torture test them. I abused that bullet in about every way I could think of. Jumped it long distances, seated it deep and shallow, heavy powder charges, you name it. While performing load work ups in the past six years I have shot well in excess of 10,000 of these bullets in about 100 different barrels from most all of the manufacturers.

I have yet to blow up a single one. I have found this to be a really good bullet. I have only one minor criticism of this bullet and that is it "pressures up" a little more than either the Sierra B. T. or the two VLDs. This pressure issue may due to its

thick jacket and its greater bearing surface than either VLD. Obviously, this requires less powder charges to assure primer retention. I can usually get away by cutting powder charges by about a half grain but in some cases I have to cut a full grain. I have never had to go below 23.2 grains of powder with this bullet in any barrel when using new military brass with crimped primers. Typical loads will be 23.5- 23.8 grains of RL15 or VV N140.

I can seldom hold primers with charges exceeding 24.1 gr. in summer temperatures approaching 100 degrees. This will result in muzzle velocities of between 2,500-2,600 fps depending on the specific characteristics of the barrel in question. So, some of these guns will shoot the Bergers from 600-1000 yards with the same load while others will be coming in a little slow for optimal 1000 yard performance. Closely watch your chronograph if you are interested in shooting these at 1000.

Unfortunately, this bullet was furloughed by Berger in January of 2013 along with a lot of other really good bullets. The factory still has all the equipment to make limited runs of the bullet for those in a buying position to order enough to warrant tooling back up. If you are having trouble finding this bullet, contact me at or see me on Commercial Row at Camp Perry during the CMP Service Rifle phase of the Nationals in Building 910-A and I’ll provide you with a source.

Barrel Recommendations The Berger 90 grain boat tail will shoot well in almost all of the barrels described in Part Two of this series. Three barrels really shine, however, and I am building all of my guns with these. For ATC shooting, the "USAR Pattern" is available from Krieger or Bartlein. In the Krieger this will be a four groove configuration with their normal 0.218" tight bore with the deeper 0.2245" groove option.

The Bartlein equivalent will be either a four groove or a 5R with a tight 0.218" bore and a deep 0.2245" groove. In both cases specify the half thousandths deeper 0.2245 groove when you order the blanks. Normal AR-15 groove depths are 0.2240" but those don’t perform as well with the Berger 90 B. T. as the deep groove option. With Krieger and Bartlein you normally just get a blank which has to be sent off to be turned and chambered.

I get both of these in chrome-moly steel and have them coated inside and out with Isonite from MMI Trutec (trutecind.com, Unlike bluing applied only to the outside of gun barrels, Trutec salt bath nitriding also protects the bore. Barrels treated with this process clean up easier than any barrels I have ever worked with and resist corrosion. There are some claims of improved wear with coated barrels and I am evaluating that presently. As mentioned previously, the deep 0.2245" grooves help with pressure issues.

You may be able to hit 2,600 fps with some of these barrels. Just watch your chronograph. Using the Krieger and Bartlein bore options I’m seeing both are currently showing very good wear characteristics. Using new factory match 77 grain ammo my rapid fire performance is a dead tie between my old 1:8 twist 80 grain gun and my newer 6.5 twist. I think that ammo quality may be the limiting factor here. Wind proofing with the 90s is about 17% greater and my group sizes are 7.7% tighter.

With the Krieger and Bartlein options listed above, fliers happen half as often with the 90 grainers at half the severity as the 80 grain loads. This is very important! If you vary from the two options listed above your chances of shooting fliers goes up as does their severity. Both deep groove tight bore options were developed originally to be "Sierra friendly". It was only by meticulous record keeping that I discovered how well these two barrels optimize the 90 grain Berger boat tails.

For those of you who want to be sure of hitting 2,600 fps with the Berger 90 grain boat tail for 1000 yard shooting you will want to go with the 6.6 twist Brux narrow land option. The narrow lands really cut pressures effectively while maintaining accuracy. I get these with Wylde chambers and have them coated with Isonite. I load these with 24.4 grains of either RL15 or VV N140.

These barrels will also shoot 77s well if you want to use them for regular ATC shooting, though their throats seem to erode faster than the Krieger and Bartlein options. Given the amount of 1000 yard Service Rifle shooting that most people do in a year, this may not be a big issue. Norm Brux says he has about 1,000 narrow land barrels of all calibers in circulation and has many reports of 4,000 round longevity. Norm’s narrow land barrels come with tall 0.218" lands and conventional 0.2240 grooves.

Another excellent choice for shooting 90s at 1000 yards is the Bartlein gain twist. Starting the bullet rotating slowly at the chamber helps over come inertia, thus lowering pressure, allowing a bit more powder (about half grain in my experience) to pick up muzzle velocity about 50 fps. I am loading the same powder charges in my gain twist barrels (24.4 grains) and achieving velocities of 2,600 fps with no chamber pressure issues. That keeps bullets really strong (1,249 fps) clear to 1000.

I suggest that you order the Bartlein Gain Twists with the tall 0.218" land and deep 0.2245" groove. I believe the Bartlein gain twist barrel may give you better wear characteristics than the Brux narrow land barrel. The Bartleins also shoot 77s for rapid fire really well. I have been torture testing some of the old Sierra 90s in the gain twists and haven’t yet blown one up.

RKS Enterprises up in Canada also supplies six groove, single point cut gain twist blanks as specified above in less than half the time if you’re in a hurry. AG