With the increased interest in the 6.5 Grendel cartridge and Grendel-based wildcats (such as the 6mmAR and 30 Major), today we’ve re-released a review by Robert Whitley.
Robert Whitley of AR-X Enterprises, LLC builds match-grade uppers for AR-platform rifles. Many of Robert’s favorite chamberings are based on the 6.5 Grendel case necked-down to 6mm. Until 2011, Lapua was the only source for 6.5 Grendel brass. As you’d expect, Lapua’s Grendel brass is truly excellent, but it is also pricey, and sometimes hard to find. Now Hornady is producing USA-made 6.5 Grendel brass. Robert Whitley has worked with the Hornady 6.5 Grendel brass for over a year now and he is able to assess its performance compared to the original Lapua version. Writing in our Shooters’ Forum, Robert reveals: “It’s decent brass but hot loads will loosen the primer pockets fast. With moderate loads you will get good case life and service from the brass and it can deliver excellent accuracy as well. Not Lapua but not bad either.”
Robert reports: “I was able to get my hands on some of Hornady’s 6.5 Grendel brass. My big question was how it would measure up, particularly the loaded necks, and whether it would be compatible with our existing 6mmAR and Turbo 40 die sets. As it turns out, this brass looks like a perfect fit for our existing die sets (and obviously 6.5 Grendel die sets too). Accordingly, folks with existing die sets will be able to use the Hornady brass without any issues.” However, as the loaded neck on the Hornady brass is .001″ (one-thousandth) slimmer than Lapua brass, you may want to try a smaller bushing when sizing Hornady Grendel brass.
The Hornady 6.5 Grendel brass has a LARGE Flash Hole, about .078″ versus .0591″ for Lapua brass. Dimensionally, the biggest difference is the shoulder diameter, with the Hornady brass measuring 0.428″ vs. 0.424″ for the Lapua brass. The Hornady is actually a better fit for 6mmAR chambers which are about 0.432″ at the shoulder. Interestingly, case H20 capacity is virtually identical. Water capacity of new, unfired Hornady 6.5 Grendel brass is 35.1 grains, while new, unfired Lapua Grendel brass holds 35.0 grains of H20. Both brands of Grendel brass increase to about 36.0 grains H20 capacity after firing and full-length sizing.
Here are some of the particulars of the Hornady cases:
Hornady 6.5 Grendel Brass
Lapua 6.5 Grendel Brass
Flash hole diameter: ~ .078″
OAL of brass: Average 1.515″
Weight of cases: 111.7 to 113.0 grains
Web diameter, unfired: 0.4375″
Shoulder diameter, unfired: 0.428″
Loaded neck diameter: 0.2895″
6mmAR loaded neck: 0.270″
Flash hole diameter: 1.5mm (0.0591″)
OAL of brass: Average 1.515″
Weight of cases: 111.0 to 112.5 grains
Web diameter, unfired: 0.4385″
Shoulder diameter, unfired: 0.424″
Loaded neck diameter: 0.290″
6mmAR loaded neck: 0.271″
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AR-platform rifles can be maintenance-intensive beasts. But some AR owners make the situation worse by not regularly cleaning important small parts, or by using too much oily/greasy lubricants in the wrong places. A properly maintained and lubricated AR15 can shoot hundreds of rounds (between cleanings) without a problem. If you learn where (and where not) to apply lubricant, you’ll find that your AR will run more reliably and the task of cleaning the bolt and bolt carrier will be less of a burden.
Here is a good video that explains AR-15 Cleaning and Maintenance. In this 30-minute NSSF video, Gunsite Academy instructor and gunsmith Cory Trapp discusses the proper way to clean and maintain the AR-15 carbine. Very knowledgeable, Trapp provides rock-solid advice for AR owners. Along with cleaning producedures, this video explains how to inspect key components and how to function-test your AR before each shooting session.
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We’ve all heard the old adage: “Keep your powder dry.” Well, tests by Norma have demonstrated that even normal environmental differences in humidity can affect the way powders burn, at least over the long term. In the Norma Reloading Manual, Sven-Eric Johansson, head of ballistics at Nexplo/Bofors, presents a very important discussion of water vapor absorption by powder. Johansson demonstrates that the same powder will burn at different rates depending on water content.
Powders Leave the Factory with 0.5 to 1.0% Water Content
Johansson explains that, as manufactured, most powders contain 0.5 to 1% of water by weight. (The relative humidity is “equilibrated” at 40-50% during the manufacturing process to maintain this 0.5-1% moisture content). Importantly, Johansson notes that powder exposed to moist air for a long time will absorb water, causing it to burn at a slower rate. On the other hand, long-term storage in a very dry environment reduces powder moisture content, so the powder burns at a faster rate. In addition, Johansson found that single-base powders are MORE sensitive to relative humidity than are double-base powders (which contain nitroglycerine).
Tests Show Burn Rates Vary with Water Content
In his review of the Norma Manual, Fred Barker notes: “Johansson gives twelve (eye-opening) plots of the velocities and pressures obtained on firing several popular cartridges with dehydrated, normal and hydrated Norma powders (from #200 to MRP). He also gives results on loaded .30-06 and .38 Special cartridges stored for 663 to 683 days in relative humidities of 20% and 86%. So Johansson’s advice is to keep powders tightly capped in their factory containers, and to minimize their exposure to dry or humid air.”
Confirming Johansson’s findings that storage conditions can alter burn rates, Barker observes: “I have about 10 pounds of WWII 4831 powder that has been stored in dry (about 20% RH) Colorado air for more than 60 years. It now burns about like IMR 3031.”
What does this teach us? First, all powders start out with a small, but chemically important, amount of water content. Second, a powder’s water content can change over time, depending on where and how the powder is stored. Third, the water content of your powder DOES make a difference in how it burns, particularly for single-base powders. For example, over a period of time, a powder used (and then recapped) in the hot, dry Southwest will probably behave differently than the same powder used in the humid Southeast.
Reloaders are advised to keep these things in mind. If you want to maintain your powders’ “as manufactured” burn rate, it is wise to head Johannson’s recommendation to keep your powders tightly capped when you’re not actually dispensing charges and avoid exposing your powder to very dry or very humid conditions. The Norma Reloading Manual is available from Amazon.com.
Real-World Example — “Dry” H4831sc Runs Hotter
Robert Whitley agrees that the burn rate of the powder varies with the humidity it absorbs. Robert writes: “I had an 8-lb. jug of H4831SC I kept in my detached garage (it can be humid there). 43.5-44.0 gr of this was superbly accurate with the 115 Bergers out of my 6mm Super X. I got tired of bringing it in and out of the garage to my house for reloading so I brought and kept the jug in my reloading room (a dehumidified room in my house) and after a few weeks I loaded up 43.5 gr, went to a match and it shot awful. I could not figure out what was going on until I put that load back over the chronograph and figured out it was going a good bit faster than before and the load was out of the “sweet spot” (42.5 – 43.0 gr was the max I could load and keep it accurate when it was stored in less humid air). I put the jug back in the garage for a few weeks and I now am back to loading 43.5 – 44.0 gr and it shoots great again. I have seen this with other powders too.”
If you have two jugs of the same powder, one kept in a room in your house and one somewhere else where it is drier or more humid, don’t expect the two jugs of the same lot of powder to chrono the same with the same charge weights unless and until they are both stored long enough in the same place to equalize again.
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In our Shooters’ Forum, one member recently asked: “What makes an AR accurate? What parts on an AR can really affect accuracy — such as free-floating handguards, barrels, bolts, bolt carriers?” He wanted an honest, well-informed answer, not just sales pitches. Robert Whitley posted a very comprehensive answer to this question, based on his experience building and testing dozens of AR-platform rifles. Robert runs AR-X Enterprises, which produces match-grade uppers for High Power competitors, tactical shooters, and varminters.
Building an Accurate AR — What is Most Important
by Robert Whitley
There are a lot of things that can be done to an AR to enhance consistent accuracy, and I use the words “consistent accuracy” because consistency is a part of it (i.e. plenty of guns will give a couple great 5-shot groups, but won’t do a very good 10- or 20-shot groups, and some guns will shoot great one day and not so good on others).
Here are 14 key things we think are important to accuracy.
1. Great Barrel: You’ll want a premium match-grade barrel, well-machined with a good crown and a match-type chambering, true to the bore and well cut. The extension threads must also be cut true to the bore, with everything true and in proper alignment.
2. Rigid Upper: A rigid, heavy-walled upper receiver aids accuracy. The typical AR upper receiver was made for a lightweight carry rifle and they stripped all the metal they could off it to make it light to carry (which is advantageous for the military). The net result are upper receivers that are so thin you can flex them with your bare hands. These flexible uppers are “strong enough” for general use, but they are not ideal for accuracy. Accuracy improves with a more rigid upper receiver.
Our friend Robert Whitley of ARX Enterprises LLC has learned, through careful measurement and testing, that some barrels threaded 5/8″ x 24 tpi at the muzzle may not deliver optimal accuracy. The reason is that the end of the barrel can bell out slightly, like a trombone, because too much steel has been removed. This is particularly true with .30-caliber barrels, but it can also be a problem with smaller caliber barrels (even 6mm). Robert demonstrates this phenomenon in the video below. All gunsmiths, and anyone considering threading a barrel, should watch the video. At 1:00 – 1:30 Robert gauges a 5/8″ x 24-threaded .30-Caliber barrel. You can see the belling effect clear as day.
“When setting up a commercial barrel in the lathe, we noticed that the maximum-sized bushing that would fit in the bore at the chamber end was almost .0015” smaller [than what would fit] at the muzzle. That precipitated my pin-gauging of a number of different commercial barrels that were threaded for 5/8” x 24 tpi. What I found is what’s shown on the video.” – R. Whitley
Solve Problem with a Larger Thread Diameter
If 5/8″ x 24 threading is potentially harmful to accuracy, is there a solution? Yes, you simply need to leave a little more steel on the barrel. (See Video starting at 02:40.) Frank Green of Bartlein barrels states: “We get these questions all the time. I say run the largest thread diameter that is possible.” Robert Whitley has found that a 3/4″ x 28 tpi threading does not cause the “belling effect”. Accordingly Robert recommends 3/4″ x 28 if you need to thread your barrel for a muzzle brake or suppressor. Robert explains: “We only make 3/4” x 28 tpi muzzle brakes and that’s what we recommend to customers.”
“See how much meatier the 3/4″ threading is vs. the 5/8″. The 3/4″ threading offers a lot more metal around the bore. There’s a lot less opportunity for the bore to become bell-mouthed…” – Robert Whitley
Barrel Threading Diameter — What’s Important to Know By Robert Whitley
In truth, the 5/8” x 24 tpi threading never came out of any accuracy-based think tank or set-up, it’s a military .30-Cal threading for barrels that someone has to carry around (they needed to keep the barrel weight down so it was smaller in diameter and the threading had to work with that situation). People have somehow assumed because the military uses that threading for certain things that it must mean that it’s also fine for a highly accurate rifle too, but that’s not really correct.
I don’t think there is any better and realistic option than the 3/4” muzzle threading, and we also do it so there is no relief cut behind the threads on the barrel (i.e. put the relief cut on the brake or jam nut, don’t chop down on the muzzle of the barrel). For some reason many have a hard time grasping that the metal at the muzzle end of a rifle is “sacred” and you should not cut it down any more than absolutely necessary. A little threaded pencil diameter nub on the end of a barrel is not ideal for accuracy especially if it’s threaded and you need to torque on it. I cringe when I see a barrel with something like an MTU or Heavy Varmint contour, only to have an itty-bitty pencil thin threaded nub right at the muzzle so someone can “screw on a can” or a muzzle brake.
Lessons Learned Over the Years
A number of years ago I did a 30BR rifle project with Craig Kostyshyn who was big in the 30BR game and he made some of the best 30BR rifle barrels for benchrest competition. When I did the project I wanted a medium-heavy Palma type contour barrel I could use and also have a muzzle turndown for a front sight band. When he found out I was going to have the muzzle turned down he said “whoa, I need to provide for that when I make the barrel because if you turn the front down later you’ll be shooting a trombone” (i.e. the muzzle bore dimension would open up).
What he did was rough contour the barrel with the turndown (about .010” oversize) before he lapped the barrel, then when he lapped the barrel he took it easy in the muzzle area and worked the back of the barrel more. I thought he was a little bit excessive in his concerns but the barrel shot great and I wasn’t going to argue with him, after all he was shooting groups in the ones. I kind of just filed that away and never thought about it until recently when I went to have Fred from Sabreco do some chamber re-work on a commercial .30-caliber barrel I had. When setting up the barrel in the lathe and indicating things Fred noticed that the maximum-sized bushing that would fit in the bore at the chamber end was almost .0015” smaller [than what would fit] at the muzzle and he mentioned it to me. That precipitated my pin- gauging of a number of different commercial barrels I had that were threaded for 5/8” x 24 tpi. What I found is what’s shown on the video.
NOTE: This is a copyrighted article. Do not reproduce or re-link more than 75 words without written permission from AccurateShooter.com.
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Editor’s Note: We originally ran this story in 2010. Since then we have had many reader inquiries about using .22-250 Lapua brass for a 6mm cartridge. Well our friend Robert Whitley worked hard on that concept a few years back, when Lapua .22-250 brass first became available. He came up with a nice 30°-shoulder wildcat that matches the accuracy of the best mid-sized 6mm cartridges. Read all about Whitley’s 6mm-250 Imp 30 below.
Our friend Robert Whitley of 6mmAR.com has come up with a new, accurate 6mm wildcat based on the new Lapua .22-250 brass that has just started arriving. Robert provides this report:
“I just received a box of the new Lapua .22-250 cases — beautiful brass! My real desire with it was to make it into a 6mm version, preferably something that was ‘no neck-turn’ with a .308 Win-type body taper that would work well in bolt gun and semi-auto magazines and would have a capacity to allow superior velocities. I considered the 6XC, but since you have to bring a whole lot of the shoulder of the brass up into the neck (when you re-form the brass from .22-250 to 6XC) that would necessitate neck-turning it because with Lapua brass the shoulder metal is thicker than neck metal of the brass.
I wanted a simple ‘neck it up and shoot it’ approach so I made up a 6mm-250 Improved 30 cartridge (i.e. 6mm-250 Improved with a 30 degree shoulder) and this thing works great — just neck up the brass, load it and shoot it! The case is like a 6XC with a .030″ longer body and a .030″ shorter neck, which works out fine if you are going to be shooting mainly the 105-108 gr bullets (which it will do very well shooting 2950 – 3000 fps). If you want to hot-rod things, which I do not, I am certain the case can push the 105-108 gr bullets a fair amount faster.
I set it up and throated the reamer for the Sierra 107s and the Berger or JLK 105 VLDs (i.e. a .090″ free bore on the reamer) and it works great with them. If I was going to use it with the Lapua 105s or the Berger 108s I would add about .025″ – .030″ to the freebore of the reamer (i.e. make the freebore around .115″ to .120″).
The great thing is you can use a 6XC die set for it without modification, and all you need to do is keep the dies about .030″ up off the shell holder from their normal position and use them as is. You can make a spacer washer about .030″ thick that you can put on and take off the 6XC dies and use the dies for both cartridges (i.e. 6XC and 6mm-250 Imp 30).
6mm-250 Imp 30 Shows Great Accuracy
Fire-forming loads are real accurate. Here is a 10-shot group I shot prone at 100 yards shooting fire-forming loads with it — the group is the size of a dime. For fire-forming I use a milder, but still very accurate load: 32.0 grains of N140 with a Sierra 107 and a BR2 primer. For fire-formed cases you can jump up to N160 (around 38-40 grains — depending on lot) and it will push the 105-108 gr bullets real accurately in the 2950-3000 fps range, with low ES and SD. This cartridge has a neck length of .268″ which is plenty long for a 6mm shooting bullets with varying bearing surface lengths. The reamer diagram (link below) leaves about a .003″ neck clearance over a loaded round, which seems to work out very well for a ‘no-turn neck’ set-up.
So there you have it … the 6mm-250 Imp 30 is simple, easy to make, accurate as all get out, there are available factory die sets you can use, and it uses great new Lapua brass — what’s not to like!”
TECH TIP by Robert Whitley,AR-X Enterprises LLC
Over the years, while working with various AR-15 cartridges that require a larger bolt-face bolt (i.e. bigger than a 5.56 NATO/.223 Rem bolt-face, like those cartridges that use a 6.8 SPC bolt or the bolt face suitable for the 6.5 Grendel-based cartridges), I have found that there is an increased potential for a certain type of jam if a modification to the standard “Mil-Spec”, square-edged ejector is not made.
The original AR-15 square-edged ejector design was made for a much smaller-diameter bolt face and the smaller diameter 5.56 NATO/.223 Rem case, and it works perfectly in that application. However, as people have adapted the AR-15 platform to shoot bigger cartridges, some parts have been modified to accept the larger cartridges (i.e. bigger bolt-face bolts for the 6.8 SPC and the 6.5 Grendel, and different extractors), yet other parts have been all but ignored. One of these “ignored” parts has been the ejector. Most of the larger-bolt-face AR-15 bolts still use the standard “Mil-Spec”, square-edged 5.56 NATO/.223 Rem. ejector. That’s the problem. But there is a simple, reliable fix!
Chamfering AR Ejector for Improved Reliablity with 6mm, 6.5mm and 6.8mm Cartridges
With the larger bolt face and the larger-diameter AR cases, the old-style “Mil-Spec” ejector can cause infrequent but still annoying jams if the ejector is not modified. The jam can occur when a cartridge case feeds up and out of the right side of the magazine, and as it does so, the back of the case must slide across the bolt face and sideways over top of the ejector if it is to center up to the chamber and feed in. If the side of the case catches on the sharp-edged ejector you can get a jam. (See picture above).
Fortunately there is an easy fix for this. One way is to take the ejector out and spin it in a lathe or cordless drill and machine or grind it and round or chamfer the sharp edge. (See picture of rounded ejector next to square edged ejector).
Quick Fix Alternative — Bevel Your Ejector
Another “quick fix” is to leave the ejector in the bolt and chamfer the sharp edge with something like a Dremel tool. (See picture). This fix is easy to do and permanently resolves this potential feeding jam issue. There are no downsides to this modification if done right and I would recommend this modification for the ejectors in all larger bolt-face AR-15 bolts.
This gunsmithing tip provided by Robert Whitley of AR-X Enterprises LLC, 199 North Broad Street, Doylestown, PA 18901. Phone: (215) 348-8789. Website: 6mmAR.com.
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Robert Whitley of AR-X Enterprises has a new .30-caliber cartridge for AR-platform rifles. The new 30 ARX is based on the 6.5 Grendel parent case necked-up to .30 caliber. The 30 ARX mag-feeds flawlessly in an AR15, while offering excellent accuracy, good velocity, and serious knock-down power. Compared to a 300 AAC Blackout (300 BLK), the new 30 ARX holds much more powder so it can push bullets faster and harder. Whitley’s 30 ARX boasts 57% more case capacity than a 300 Blackout. As a result, the 30 ARX outperforms the 300 BLK by a large margin. In a 20″-barreled AR, the 30 ARX can drive a 125gr bullet at 2500+ fps, or launch a heavier 150gr bullet at 2400+ fps:
30 ARX Loads
H4198, CCI BR4 Primers,
Necked-up Lapua 6.5 Grendel Brass:
2419 FPS: 28.0 gr. H4198, Nosler 125gr Ballistic Tip Hunting Bullet (2.260″ OAL)
2517 FPS: 29.0 gr. H4198, Nosler 125gr Ballistic Tip Hunting Bullet (2.260″ OAL)
2363 FPS: 28.0 gr. H4198, Sierra 150gr BT Hunting Bullet (2.240″ OAL)
2441 FPS: 29.0 gr. H4198, Sierra 150gr BT Hunting Bullet (2.240″ OAL)
Robert Whitley explains the advantanges of the 30 ARX for AR-platform rifles: “The 30 ARX is a cartridge designed from the get-go for use in an AR-15. The case length and chamber design of the 30 ARX are optimal. The case allows the use of many of the favorite .30-cal bullets, magazine fed out of an AR-15 and backed by some real power. Brass is easy to make with a simple necking-up process. Neck it up, load it and go shoot. Good 6.5 Grendel brass is readily available, and we have 30 ARX dies available.”
Watch One-Step Process for Forming 30 ARX Case from 6.5 Grendel Brass
With the ability of Lapua 6.5 Grendel brass to handle stout loads, the 30 ARX cartridge delivers 30-30 Winchester-class performance, from the modern, semi-auto AR-15 platform. The 30 ARX cartridge has sufficient case capacity to push popular .30-cal bullets fast and accurately even at moderate chamber pressures. The case has approximately 38 grains water capacity. With its 57% greater capacity than a 300 Blackout, the 30 ARX is a more versatile, more powerful hunting cartridge (at least when loaded to supersonic speeds). With 150gr bullets running in the 2500 fps range, the 30 ARX offers impressive knockdown power in a cartridge that fits an AR-15 magazine.
30 ARX Cartridge OAL mag-feeds perfectly with a variety of .30-cal bullets.
Longer, heavier long-range bullets (with longer COAL) can be single-loaded.
Lapua 6.5 Grendel brass is excellent, strong brass, that is readily available.
AR-X Enterprises now offers die sets for the 30 ARX.
The neck up process is very easy. Simply lube the inside of the necks of 6.5 Grendel brass, run the brass through your re-size die (with .30 Cal expander in place).
Works well with a lot of commonly available powders such as: Hodgdon 4198, Vihtavouri N130, Accurate LT-32, Accurate AA1680.
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Robert Whitley of AR-X Enterprises, LLC builds match-grade uppers for AR-platform rifles. Many of Robert’s favorite chamberings are based on the 6.5 Grendel case necked-down to 6mm. Until 2011, Lapua was the only source for 6.5 Grendel brass. As you’d expect, Lapua’s Grendel brass is truly excellent, but it is also pricey, and sometimes hard to find. Now Hornady is producing USA-made 6.5 Grendel brass. Robert Whitley has worked with the Hornady 6.5 Grendel brass for over a year now and he is able to assess its performance compared to the original Lapua version. Writing in our Shooters’ Forum, Robert reveals: “It’s decent brass but hot loads will loosen the primer pockets fast. With moderate loads you will get good case life and service from the brass and it can deliver excellent accuracy as well. Not Lapua but not bad either.”
Robert reports: “I was able to get my hands on some of Hornady’s 6.5 Grendel brass. My big question was how it would measure up, particularly the loaded necks, and whether it would be compatible with our existing 6mmAR and Turbo 40 die sets. As it turns out, this brass looks like a perfect fit for our existing die sets (and obviously 6.5 Grendel die sets too). Accordingly, folks with existing die sets will be able to use the Hornady brass without any issues.” However, as the loaded neck on the Hornady brass is .001″ (one-thousandth) slimmer than Lapua brass, you may want to try a smaller bushing when sizing Hornady Grendel brass.
The Hornady 6.5 Grendel brass has a LARGE Flash Hole, about .078″ versus .0591″ for Lapua brass. Dimensionally, the biggest difference is the shoulder diameter, with the Hornady brass measuring 0.428″ vs. 0.424″ for the Lapua brass. The Hornady is actually a better fit for 6mmAR chambers which are about 0.432″ at the shoulder. Interestingly, case H20 capacity is virtually identical. Water capacity of new, unfired Hornady 6.5 Grendel brass is 35.1 grains, while new, unfired Lapua Grendel brass holds 35.0 grains of H20. Both brands of Grendel brass increase to about 36.0 grains H20 capacity after firing and full-length sizing.
Here are some of the particulars of the Hornady cases:
Hornady 6.5 Grendel Brass
Lapua 6.5 Grendel Brass
Flash hole diameter: ~ .078″
OAL of brass: Average 1.515″
Weight of cases: 111.7 to 113.0 grains
Web diameter, unfired: 0.4375″
Shoulder diameter, unfired: 0.428″
Loaded neck diameter: 0.2895″
6mmAR loaded neck: 0.270″
Flash hole diameter: 1.5mm (0.0591″)
OAL of brass: Average 1.515″
Weight of cases: 111.0 to 112.5 grains
Web diameter, unfired: 0.4385″
Shoulder diameter, unfired: 0.424″
Loaded neck diameter: 0.290″
6mmAR loaded neck: 0.271″
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In our Shooters’ Forum, one member posed the question: “What makes an AR accurate? What parts on an AR can really affect accuracy — such as free-floating handguards, barrels, bolts, bolt carriers?” He wanted an honest, well-informed answer, not just sales pitches. Robert Whitley posted a very comprehensive answer to this question, based on his experience building and testing dozens of AR-platform rifles. Robert runs AR-X Enterprises, which produces match-grade uppers for High Power competitors, tactical shooters, and varminters.
Building an Accurate AR — What is Most Important
by Robert Whitley
There are a lot of things that can be done to an AR to enhance consistent accuracy, and I use the words “consistent accuracy” because consistency is a part of it (i.e. plenty of guns will give a couple great 5-shot groups, but won’t do a very good 10- or 20-shot groups, and some guns will shoot great one day and not so good on others).
Here are things we think are important to accuracy.
1. Great Barrel: You’ll want a premium match-grade barrel, well-machined with a good crown and a match-type chambering, true to the bore and well cut. The extension threads must also be cut true to the bore, with everything true and in proper alignment.
2. Rigid Upper: A rigid, heavy-walled upper receiver aids accuracy. The typical AR upper receiver was made for a lightweight carry rifle and they stripped all the metal they could off it to make it light to carry (which is advantageous for the military). The net result are upper receivers that are so thin you can flex them with your bare hands. These flexible uppers are “strong enough” for general use, but they are not ideal for accuracy. Accuracy improves with a more rigid upper receiver.
3. True Receiver Face: We’ve found that truing the receiver face is valuable. Some may argue this point but it is always best to keep everything related to the barrel and the bore in complete alignment with the bore (i.e. barrel extension, bolt, upper receiver, carrier, etc.).
4. Barrel Extension: You should Loctite or glue the barrel extension into the upper receiver. This holds it in place all the way front to back in the upper receiver. Otherwise if there is any play (and there typically is) it just hangs on the face of the upper receiver completely dependent on the face of the upper receiver as the sole source of support for the barrel as opposed to being made more an integral part of the upper receiver by being glued-in.
5. Gas Block: You want a gas block that does not impose pointed stress on the barrel. Clamp-on types that grab all the way around the barrel are excellent. The blocks that are pinned on with tapered pins that wedge against the barrel or the slip on type of block with set screws that push up from underneath (or directly on the barrel) can deform the bore inside of the barrel and can wreck the accuracy of an otherwise great barrel.
6. Free-Float Handguard: A rigid, free-float handguard (and I emphasize the word rigid) really makes a difference. There are many types of free-float handguards and a free-float handguard is, in and of itself, a huge improvement over a non-free-float set up, but best is a rigid set-up. Some of the ones on the market are small diameter, thin and/or flexible and if you are shooting off any type of rest, bipod, front bag, etc., a rigid fore-end is best since ARs want to jump, bounce and twist when you let a shot go, as the carrier starts to begin its cycle before the bullet exits the bore.
7. Barrel Contour: You want some meat on the barrel. Between the upper receiver and the gas block don’t go real thin with a barrel (we like 1″ diameter if it’s workable weight-wise). When you touch off a round and the bullet passes the gas port, the gas system immediately starts pressuring up with a gas impulse that provides vibrations and stress on the barrel, especially between the gas block back to the receiver. A heavier barrel here dampens that. Staying a little heavier with barrel contour through the gas block area and out to the muzzle is good for the same reasons. ARs have a lot going on when you touch off a round and the gas system pressures up and the carrier starts moving (all before the bullet exits the bore) so the more things are made heavier and rigid to counteract that the better — within reason (I’m not advocating a 12-lb barrel).
8. Gas Tube Routing Clearance: You want a gas tube that runs freely through the barrel nut, through the front of the upper receiver, and through the gas key in the carrier. Ensure the gas tube is not impinged by any of them, so that it does not load the carrier in a stressed orientation. You don’t want the gas tube bound up so that when the gas tube pressures up it immediately wants to transmit more force and impulse to the barrel than would normally occur. We sometimes spend a lot of time moving the gas block with gas tube on and off new build uppers and tweaking gas tubes to get proper clearance and alignment. Most gas tubes do need a little “tweaking” to get them right — factory tubes may work OK but they typically do not function optimally without hand-fitting.
9. Gas Port Tuning: You want to avoid over-porting the gas port. Being over-gassed makes the gas system pressure up earlier and more aggressively. This causes more impulse, and increases forces and vibration affecting the top end and the barrel. Tune the gas port to give the amount of pressure needed to function properly and adequately but no more.
10. Front/Back Bolt Play: If accuracy is the game, don’t leave a lot of front/back bolt play (keep it .003″ but no more than .005″). We’ve seen factory rifles run .012″ to .015″ play, which is OK if you need to leave room for dirt and grime in a military application. However, that amount of play is not ideal for a high-accuracy AR build. A lot of front/back bolt play allows rounds to be hammered into the chamber and actually re-formed in a non-consistent way, as they are loaded into the chamber.
11. Component Quality: Use good parts from a reputable source and be wary of “gun show specials”. All parts are NOT the same. Some are good, some are not so good, and some aftermarket parts are simply bad. Don’t be afraid to use mil-spec-type carriers; by and large they are excellent for an accuracy build. Also, remember that just because a carrier says “National Match” or something else on it does not necessarily mean it’s any better. Be wary of chrome-plated parts as the chrome plating can change the parts dimensionally and can also make it hard to do hand-fitting for fit and function.
12. Upper to Lower Fit: A good upper/lower fit is helpful. For quick and dirty fit enhancement, an Accu-Wedge in the rear helps a lot. The ultimate solution is to bed the upper to a specific lower so that the upper and lower, when together, are more like one integral unit. For the upper receivers we produce, we try to get the specs as close as we can, but still fit the various lowers in the market place.
13. Muzzle Attachments: Don’t screw up the muzzle (literally). Leave as much metal on the barrel at the muzzle as you can. People like to thread the muzzle for a flash hider, suppressor, muzzle brake, or some other attachment, but if you really want accuracy, leave as much metal as you can there. And, if you have something that screws on, set it up so that it can be put on and have it stay there without putting a lot of torque and stress on it right where the bullet exits the bore. If you are going to thread the end of the barrel, make it concentric with the bore and make sure what you screw on there is as well. For all muzzle attachments, also ensure that the holes through which the bullet passes through are dead true to the bore. Many aftermarket screw-on things are not so good that way. Anything that vents gas should vent symmetrically (i.e. if it vents left, it should vent equally right, and likewise, if it vents up, it should vent down equally). Uneven venting of gas can wreck accuracy.
14. Quality Ammunition: Ammo is a whole story by itself, but loads that are too hot typically shoot poorly in an AR-15. If you want accuracy out of an AR-15, avoid overly hot loads. Shown below are test groups shot with four (4) different uppers, all with moderate loads. These four uppers all pretty much had the same features and things done to them as explained in this article, and they all shot great.
Houle Bloop Tube (Sight Extension) Gear Reviewby Robert Whitley
As a competitive shooter and a builder of custom AR-15 accuracy competition uppers, one of the frequent requests I have from shooters is for a recommendation for a good bloop tube. What people want is a bloop tube that is light and strong, one that has no detrimental effect on accuracy, one that works well with many of the existing front sights, and can be removed and re-attached quickly and easily with no loss of zero. For years finding a bloop tube that fulfills all these requirements has been a somewhat elusive exercise. I am pleased to report that I have found the Houle Bloop Tube to meet all my requirements. In my opinion, this is the best bloop tube on the market, by far. You can order a Houle tube from Norm’s Website, TopGunRI.com or e-mail Norm at topgunngh [at] verizon.net.
Bloop Tubes Designed by a National Champion
Norm Houle is a High Power and long-range shooter who has used these tubes to win National High Power Rifle Championships multiple times in past years. This past summer at Camp Perry, Norm’s bloop tubes were used by top “podium level” shooters in various events, including David Tubb, who won the National Long Range Championship using one of Norm’s tubes. Rodrigo Rosa also used Houle tubes this year to place second in the National High Power Rifle Championship and third in the Long Range National Championship.
I have a couple of Norm Houle’s bloop tubes that I have used with a couple of rifle projects. Here are some of my thoughts on installation and use of the Houle Bloop Tubes:
Accuracy with the tubes in place is excellent!
The tube assemblies are two piece clamp-on tube assemblies, and the bloop tubes can be removed and re-attached with no loss of zero (and I mean no loss of zero). This is a big one! Over the years I have had quite a few clamp on tubes, but few of them repeated like these.
The tubes are very light but also very strong and low profile. Some of the clamp-on bloop tubes I have had over the years were huge, heavy and provided a large side profile (crosswind sail factor for offhand, etc.).
Norm offers 2″, 4″, and 6″ bloop tube lengths. The tubes are made to work with a .750″ dia. muzzle turn down and both of the ones I have work perfectly with a minimum turndown of 1.625″ long which provides enough “front-back” distance to permit the locating ring and bloop tube to be properly mounted on the barrel at the same time and work as they should. The tubes are also set up to use front sights set up to mount on a .750″ diameter mounting.
Each tube assembly has a clamp-on locating ring plus a clamp-on bloop tube that positively indexes off a tapered pin that protrudes from the locating ring. The locating ring is light but very strong and absolutely stays put when you clamp it on the barrel end (clamps on with one screw using a common 7/64″ Allen wrench). The bloop tube part of the assembly has two clamp-on screws (use a common 7/64″ Allen to put on, mount and take off).
Using Different-Length Tubes for Different Applications You can buy one tube with two or more locating rings and set multiple rifles up so you can move your bloop tube (with front sight attached) from rifle to rifle. You can also use two different bloop tubes to mate up with one locating ring on the same rifle. Norm uses a 2″ tube (with a front sight attached) for offhand and rapid sitting at 200 yards (short tube minimizes crosswind sail factor). For 300-yard rapid prone and 600-yard slow prone, Norm takes off the 2″ tube and mounts a 6″ tube on the rifle (with a front sight attached to it). Norm switches back and forth as needed from match to match (a 4″ tube is also offered). Norm noted that Rodrigo Rosa also used the same Houle bloop tube set-up with two different tubes this year at Perry to take second overall.
The price of a Houle bloop tube assembly with locating ring is $125.00. That’s more than some other brands, but a good value considering the design, features, and high-quality construction of Norm’s bloop tubes. Just as with all sights and optics… you get what you pay for.
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by Robert Whitley After Accurate Shooter published the July 31, 2010 Daily Bulletin feature on 6mm BRX Myth-Busting With Bob Crone, further research reveals that there’s more to tell about the BRX, its origins, and its original specifications.
6 BRX Myth-Busters Follow-Up Challenge
I wanted to obtain a print reflecting the true original dimensions of Bob Crone’s 6mm BRX reamer. I hoped to verify the head spacing of the reamer to be .100″ longer than a 6mm BR, and I also wanted to see how Bob’s original print compares to 6mm BRX match reamers currently considered to be the “standard in the industry”.
Recreating the Original 6mm BRX Reamer Print
Clymer Precision was contacted to obtain a print of Bob’s original reamer. Todd Wilms, the current owner of Clymer Precision (and a heck of a nice guy as well) went back in the Clymer archives and pulled the records of the dimensions of Bob Crone’s 6mm BRX reamer. Todd then entered them into Clymer’s current reamer drawing program and has generated a current drawing reflecting the original 6mm BRX reamer. The print (see below) confirms the head space of the 6mm BRX to be .100″ longer than a 6mm BR (i.e. 1.267″ min at a shoulder datum diameter of .350″).
Comments on Bob’s 1996 Clymer Reamer
In many ways, the print dimensions are very close to what is currently recognized as the “standard in the industry” for 6mm BRX reamers, however in other ways there have been some definite changes:
A. Body Diameter: A chamber body diameter of .470″ is still in wide use today with 6mm BRX reamers (that’s measured .200″ forward of the bolt face). The current Lapua 6mm BR brass has a web diameter very close to this diameter and one should be wary of trying to tighten this dimension. If anything, running a little looser (like the .4708″ dimension similar to that used with the 6mm Dasher) would not hurt the performance of the 6mm BRX cartridge a bit.
B. Shoulder Diameter: Bob’s original reamer had a shoulder diameter of .4609″ (the same as a 6mm BR Norma), however many current 6mm BRX reamers now use a .460″ shoulder diameter which helps avoid overworking the brass there if readily available commercial dies are used.
C. Max Chamber Length: Bob’s original print had a “max chamber length” of 1.570″ (the same as a 6mm BR Norma), however many of the current 6mm BRX reamers have shortened this up a little. This is because, when 6mm BR brass is fire-formed into 6mm BRX brass, typically the brass shortens. Indeed, this author’s 6mm BR brass shrinks in OAL from around 1.555″ to around 1.547″ when it is fire-formed to 6mm BRX brass. A max chamber length in the range of 1.560″ – 1.565″ is seen often with 6mm BRX reamers these days.
D. Neck Diameter: While Bob’s reamer has a .262″ neck, this has for the most part given way to either a .269″ (sometimes .268″) turned neck, or a .272″ (sometimes .271″) no-turn neck, with the neck diameter typically selected based on the actual dimensions of the brass to be used.
E. Throat Angle: Bob’s throat angle was one and a half degrees, which seems to be standard and in wide use today with the 6mm BRX.
F. Freebore: Bob’s freebore length was 0.00″ because his smith used a separate throater to set the throat length Bob wanted for specific bullets. These days, a built-in freebore in the range of .104″ – .125″ seems to be very common with 6mm BRX reamers. Freebore in that range is seen by many as a good choice for the readily available 105- to 108-grain 6mm bullets.
6mm BRX — Real World Specs
Here are measurements on Robert Whitley’s 6mm BRX brass, as fire-formed, full-length sized and ready to load in a no-turn chamber.
Base to shoulder = 1.170″
Base to neck/shoulder junction = 1.333″
Overall case length (fired 2x and re-sized 2x) = 1.547″
Shoulder diameter (resized) = .459″
Diameter .200″ forward of base (resized) = .470″
Neck diameter loaded = .269″
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Robert reports: “I was able to get my hands on some of Hornady’s 6.5 Grendel brass. My big question was how it would measure up, particularly the loaded necks, and whether it would be compatible with our existing 6mmAR and Turbo 40 die sets. As it turns out, this brass looks like a perfect fit for our existing die sets (and obviously 6.5 Grendel die sets too). Accordingly, folks with existing die sets will be able to use the Hornady brass without any issues.” However, as the loaded neck on the Hornady brass is .001″ (one-thousandth) slimmer than Lapua brass, you may want to try a smaller bushing when sizing Hornady Grendel brass.
Tests Show Burn Rates Vary with Water Content
Our friend Robert Whitley of 
6mm-250 Imp 30 Shows Great Accuracy
Robert Whitley of 
5. Gas Block: You want a gas block that does not impose pointed stress on the barrel. Clamp-on types that grab all the way around the barrel are excellent. The blocks that are pinned on with tapered pins that wedge against the barrel or the slip on type of block with set screws that push up from underneath (or directly on the barrel) can deform the bore inside of the barrel and can wreck the accuracy of an otherwise great barrel.
Bloop Tubes Designed by a National Champion
You can buy one tube with two or more locating rings and set multiple rifles up so you can move your bloop tube (with front sight attached) from rifle to rifle. You can also use two different bloop tubes to mate up with one locating ring on the same rifle. Norm uses a 2″ tube (with a front sight attached) for offhand and rapid sitting at 200 yards (short tube minimizes crosswind sail factor). For 300-yard rapid prone and 600-yard slow prone, Norm takes off the 2″ tube and mounts a 6″ tube on the rifle (with a front sight attached to it). Norm switches back and forth as needed from match to match (a 4″ tube is also offered). Norm noted that Rodrigo Rosa also used the same Houle bloop tube set-up with two different tubes this year at Perry to take second overall. 
After Accurate Shooter published the July 31, 2010 Daily Bulletin feature on 
