Whitley Crafts a Tack-Driving, Bag-Riding 20-Caliber Prairie Dog Rifle
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Right now, "black rifles" are probably the hottest-selling long guns in the American market. They are used for everything from home defense to long-range competition. Many AR15 owners use their rifles for varminting. With some intelligent upgrades, an AR15-based gun can be a GREAT varmint rifle--maybe the best available for prairie dogs and other small critters. This story is about a project gun built for AccurateShooter.com. We wanted to optimize an AR15 so it could out-perform any box-stock, black rifle on the varmint fields. By adding key components and fitting the gun with an ultra-accurate, 20-caliber Bartlein barrel, we've achieved something special. This gun boasts superb accuracy, great stability on the bags, low recoil, and excellent ergonomics. The 20 Practical chambering offers .204 Ruger-class ballistics using standard .223 Rem brass and easily-modified .223 Rem dies.
Robert Whitley (AR-X Enterprises, LLC.) may be contacted via his website www.6mmAR.com.
Some months ago, AccurateShooter.com and Robert Whitley decided to build a new 20-caliber AR15-based rifle. Our project goal was to create the "ultimate" semi-automatic varmint/prairie dog rifle. We wanted a low-recoiling, flat-shooting AR that worked great with a front rest and rear sandbag on a transportable field bench (such as the Coyote Jakes bench). We knew the basic, unmodified AR15 design did not work well with a pedestal rest and rear bag, so we set out to fix that with a better set-up for riding the bags. But we wanted the bag-riding components to be removable so the gun could be easily returned to standard configuration for shooting with sling or bipod. Robert worked with Evolution Gun Works (EGW) in Quakertown, PA, to develop machined Delrin bag-riding units front and rear. The 3"-wide front "sled" attaches to the threaded anchor for the sling swivel stud, while the rear bag-rider mounts in place of the standard metal rear sling loop.
Flat-Shooting 20 Practical Chambering Our Ultimate AR Varminter features a 24" Bartlein 11-twist cut-rifled barrel, DPMS side-charging upper, and a Jewell trigger. It is chambered in "20 Practical", a cartridge popularized by Warren "Fireball" Brookman. This is simply the .223 Remington necked down to .204. You can use your existing .223 brass -- no special case-forming required! The 20 Practical is accurate, flat-shooting, and has almost no recoil. The advantage over the standard .223 Remington is that, grain for grain, the bullets have a higher BC and travel at a higher velocity for more dramatic effect on a small varmint. The ultra-low recoil allows you to easily see your hits, even without a muzzle brake. The 20 Practical, launching 40-grainers at about 3750 fps, shoots flatter than a .223 Rem with 50gr hollowpoints. We review 20 Practical ballistics in a sidebar below.
Is It Accurate? You Better Believe It! Fitted with the EGW bag-riders, Jewell trigger, and a Bartlein cut-rifled barrel, this rifle hammers. Shooting from a Caldwell Fire Control Rest supplied by Battenfeld Technologies, the accuracy was remarkable, even in rapid-fire. Each of the groups shot with the 40gr Bergers and Hodgdon H335 would fit under a dime! That's superb accuracy for any varmint rifle, much less a semi-automatic. Watch the video below to see Robert shoot the gun. He drilled his last 5-shot group into 0.257".
Robert reports: "This rifle is a real shooter, as the video demonstrates. So far, each 5-shot group I've shot with the gun can be covered by a dime. I did virtually no load development, yet the rifle produced 'instant accuracy' with H335 and Berger 40gr BTHP bullets loaded about .010" off the lands (about 2.228" OAL). I did not test a wide variety of other loads because the rifle was to be sold so we wanted to keep the round count down. However, I also built a second upper along with the one for this project and the accuracy of that was excellent as well. The 20 Practical can be a very accurate chambering in the AR15."
Ideal Varmint Platform with Ultra-Low Recoil A self-loader such as the AR15 is a good choice as a prairie dog gun because it allows quick follow-up shots. Combine self-loading with ultra-low recoil (which makes it easier to see your hits) and you have a formidable weapon for working over a 'Dog town. Our 20 Practical AR is an extremely low-recoiling varminter. Robert explains: "The 20 Practical is a low-recoiling cartridge to start with, but in an AR-15, the perceived recoil is even lower than with a bolt gun of equal weight. With the direct gas impingement bleeding off energy to cycle the action, it seems like the AR15 has a built-in, recoil-reduction system. The rigidity of the receiver and hand guard also help. That keeps the muzzle on target, even without a muzzle brake. I could easily see my shots hit paper. I'm sure varmint hunters with a 20 Practical AR could see their hits when shooting a 20 Practical with bag-riders and a good rest set-up."
In the video above, you can see Robert shooting the gun for the first time. Even off a wobbly rest, without the bag-riders, the gun punches small groups. Robert reports: "The very first group shot off the bench after sight-in is shown in the above video. Keep in mind this was done with no load work-up and I shot fast to ensure the video was not too long. The load was with 26.0 grains of H335, CCI BR-4 Primers, Winchester brass, and the Berger 40-grainers going right around 3750 fps."
Stability and Accuracy with the EGW Bag-Rider System
EGW Bagrider Assembly One of the main goals with this project was to develop an affordable, easy-to-install system that would allow an AR15 to function effectively with front rest and rear sandbags. The typical AR doesn't work well on a rest because the front handguard rolls in the front rest and the rear stock is just about the worst possible shape to ride a rear sandbag. With some design ideas from AccurateShooter.com's Editor, Robert Whitley worked with the clever folks at Evolution Gun Works (EGW) to produce a set of bag-riders that could easily attach to an AR15 without gunsmithing.
EGW produced a great system consisting of front and rear Delrin blocks. The front block attaches via the swivel stud mount. Just unscrew the swivel stud, put the front bag-rider in place and attach one hex-head machine screw. The front bag-rider is contoured to match the handguard profile so it fits securely with no wobble. In the rear, the bag-rider replaces the rear sling loop. Again, installation is easy. Just remove one screw at the bottom edge of the buttplate and slide out the sling loop. The rear bag-rider has a tang that goes in the slot for the sling loop. Slide the rear bag-rider in place from the bottom (with the tang in the slot), replace the attachment screw, and you're good to go. Overall, it is a slick system. Front and rear bag-riders can be attached in a couple of minutes. The Delrin blocks slide easily in the bags and make the gun ultra-stable. The gun tracks straight back. Front and rear EGW Bag-rider blocks are sold as a set for $75.00. Front or rear pieces can be purchased individually for $40.00 each.
The 20 Practical -- Better Ballistics, 100% Function
Why did we choose the 20 Practical chambering for this rifle? Of course we wanted something innovative, but the key reason is that the 20 Practical offers better ballistics than the .223 Rem with light bullets, and the 20 Practical shares few, if any, of the drawbacks of a typical "wildcat" cartridge. In truth, the 20 Practical is about as close to a SAAMI cartridge as you can get. One can use regular .223 Rem brass, and even reload with .223 Rem dies with a few, inexpensive conversion pieces. The 20 Practical also feeds and functions with 100% reliability in standard AR15 magazines.
The skeptical reader might then ask, "Well, why not just stick with the .223 Rem in an AR?" Good question. There is nothing wrong with the .223 Rem. It is an excellent chambering. The .223 Rem can be very accurate, and very good factory-loaded ammo is available. However, for our intended purpose, namely shooting prairie dogs and other small varmints, the 20 Practical chambering offers a significant advantage. With bullets of equal weight, the 20 Practical shoots flatter, and bucks the wind better than the .223 Rem alternative. Beyond 250 yards the difference in drop and drift is quite pronounced.
Good Selection of 20-Caliber Varmint Bullets There is an excellent selection of 20-caliber varmint and match bullets that have higher ballistic coefficients than .224-class bullets of equal weight. For example, the BC of the .204-diameter 40gr Sierra Blitz-King is 0.287, while the BC of the .224-diameter 40gr Sierra Blitz-King is 0.196. The 20-Cal Blitz-King's BC is 46% better than the equivalent .224 bullet. And in the wind, BC rules. Because of the superior BCs of the 20-caliber bullets, together with their higher initial velocities, the 20-Cal projectiles exhibit less drop and less drift than do .224-caliber bullets (of similar weight). From the chart above, starting with a 200-yard zero, a 20-Cal 40-grainer launched at 3850 fps will drop 7.82" at 350 yards, while a .224-Cal 40-grainer (launched at 3600 fps) will drop 11.55" at 350 yards. That's a BIG difference. Of course, if you speed up the .224 40gr bullet, some of that gap is made up, but we've used typical max velocities* for these cartridges. Bottom line, grain for grain, the 20 Practical can shoot flatter than a standard .223 Rem.
*Hodgdon's Reloading Data Center lists 3601 fps as the velocity for a "Max Load" of H4198 and Nosler 40gr bullet in the .223 Remington. Hodgdon's H322 "Max Load" for the same bullet runs 3574 fps in the .223 Rem.
Superior Components for the Ultimate AR Varminter
Design and Gunsmithing of the Upper Receiverby Robert Whitley This upper features a rigid, heavy-walled DPMS Low Pro upper receiver assembly that was modified for a side charging handle. We like to use the heavy-walled upper receivers and feel they are best for accuracy because of their strength and rigidity. The standard military-style, flat-top upper receivers are made from excellent quality metal, but because they are made for a carry rifle, they strip as much metal off them as they can to reduce weight. The net result is that the standard flat-top upper receivers are thin and flexible and not ideal for accuracy work. About 95% of the uppers we sell are equipped with rigid, heavy-walled upper receivers because the customers are looking for accuracy and understand that a rigid upper receiver is best for that purpose.
For this project, the upper was put together in the same manner as we do the 6mmAR uppers. As with all uppers we build, the receiver face was specially trued and the barrel extension was bonded into the upper receiver with Loctite (in addition to being held in place by the barrel nut). We also are very particular as far as torque settings for the barrel extension and the barrel nut as we have found this makes a definite difference in the overall performance and accuracy of uppers. Fred Szablewski at Sabreco, Inc. in Skippack, PA, (610) 584-8228, did all the barrel work, and his work is truly excellent. Fred and I have done a lot with ARs over the years and he really 'knows his stuff' when it comes to ARs. He indicates the bore of the barrel in his lathe so that the chamber and the threading for the barrel extension are both concentric and true to the bore, and the shoulder for the barrel extension is 100% perpendicular to the bore as well. This assures everything is in full alignment and straight to the bore. He does the same with the muzzle as well so that the crown is concentric with the bore and perfect and uniform in all respects.
Heavy-Walled, Free-Floating Hand Guard for Accuracy The hand guard is a 2 1/4" round, heavy-walled aluminum free-floating design with a very durable, baked-on black powder coat finish. (Red, blue and other colors are available on request). These hand guards were developed by me with the help of George Smith at Evolution Gun Works. I prefer the 2 1/4" heavier-walled aluminum free-float hand guards because they are very rigid. In the beginning when we first started building uppers, we experimented with hand guards made from some composites and other materials. We found out that that these did not have optimum rigidity for accurate target work (they were squishy and flexible). Ultimately we contracted to have our own hand guards fabricated to meet our specifications and get the rigidity we wanted. Rigid is the way to go if you want accuracy in an AR.
Clamp-On Gas Block The upper also features a clamp-on gas block, custom-made to our specifications. For accuracy work with ARs, there is also no better gas block than a clamp-on unit. These gas blocks were developed by myself and George Smith at EGW. Years ago I noticed that the only gas blocks on the market were those that slipped over the barrel and were held in place with set screws or pins that pushed hard against the barrel (usually in one spot). Beware... those set screws can create a bulge or tight spot in the bore. Here's how I learned that. Some time ago, I attached a slip-on gas block with a set screw on a rifle. I then ran a tight-fitting patch down the bore with a jag on a cleaning rod. To my surprise I could feel the patch hit a tight spot in the bore right where the set screw for the gas block was placed. If I loosened the set screw the tight spot went away. I also have inspected barrels that have these non-clamp-on gas blocks, and have seen copper build up in the bore right where the set screws and/or pins are located. That copper is a sign of bore deformation. The clamp-on blocks completely eliminate this deformation issue. Moreover, with clamp-ons, you don't have to put them on real tight to stay put, and they completely seal off leakage around the barrel. A side benefit is that you can easily take the gas block on and off and re-adjust things if you need to service the upper. Just loosen the two clamp screws and do what you need to do. For all these reasons, the clamp-on gas block is a far superior to other designs in my view.
GG&G GS-1 Extended Rail for Proper Eye Relief If you've ever shot an standard flat-top AR with a high-magnification scope, you know that the ergonomics are all wrong. If you move your head far enough back to get correct eye relief, it's nearly impossible to shoulder the gun properly, particularly in the prone position. To allow proper eye relief AND a comfortable shooting position we needed to move the scope well forward, with the turrets slightly ahead of the front of the receiver. The answer was fitting a GG&G GS-1 mount. This is a high-quality, rock-solid set-up that mounts securely to the top of a flat-top receiver. Retail price is $89.95. An extended rail of this type is a "must-have" if you're mounting a large optic on an AR with a standard-length buttstock.
Preparing and Loading 20 Practical Brass -- It's Easy
The beauty of the 20 Practical as a cartridge is its simplicity. You can start with .223 Rem brass, and use .223 Rem dies with minor modifications. No special case-forming dies are necessary. To prepare the brass, all you need is a .223 Rem bushing die with .233" and .225" bushings, plus a 20 Cal decapping rod assembly, Redding part #14206, priced about $15. First remove the .223 Rem decapping assembly and replace it with the 20 Cal decapping rod assembly (the same assembly used with Redding .204 Ruger dies). Put the .233" bushing in a Redding Type 'S' bushing die and run your cases through for a first pass. Then swap in the smaller .225" bushing for the second pass. Now your brass is sized and ready for loading. You can seat bullets using a regular Redding .223 Rem competition seating die with no mods. Use the .225" bushing for neck sizing for all subsequent loadings once the cases have been necked down the first time. It is simple and easy.
In the accompanying video, Robert Whitley shows how to neck down .223 Rem brass using two bushings in sequence. Then he shows how to seat a bullet with the Redding Comp Seater die. To save time in the video, Robert skipped the steps of adding primer and powder. But those steps require no special equipment for the 20 Practical.
Accuracy came easy with the 20 Practical. After running a QuickLOAD simulation we determined that H335 should give good velocity and load density. Using a Hornady Lock-N-Load OAL tool, Robert measured the distance to the lands for Berger 40gr BTHP bullets. The Bergers hit the lands about 2.238" OAL, so Robert loaded his rounds to about 2.228" OAL (.010" off the lands). With a semi-auto such as the AR15, it's wise to keep your bullets off the lands. Ten-thousandths off the lands proved very accurate with the Berger 40-grainers. Even with no serious load development, each group shot with the Bergers could fit under a dime.
With the outstanding Bartlein barrel, this gun delivers easy half-MOA accuracy. With more load development (and perhaps a different powder), who knows, this AR might shoot even smaller. When Robert really concentrated, on his last 5-shot string (photo right), he posted a .257" group. Quarter-MOA from an AR? Yep it's possible.