December 15th, 2018

The Ultra-Accurate AR — Secrets of AR Accuracy Revealed

AR-X AR15 Upper

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.

AR-X AR15 Upper

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.

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.

AR-X AR15 Upper5. 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.

Robert Whitley AR Accurate accuracy aR15 barrel trigger MSR gunsmithing

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.

AR-X AR15 Upper

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.

AR-X AR15 Upper

Robert Whitley
www.6mmAR.com

Permalink - Articles, Gunsmithing, Tactical 6 Comments »
May 23rd, 2015

What Makes an AR Accurate — Whitley Offers Answers

AR-X AR15 Upper

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.

AR-X AR15 Upper

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.

(more…)

Permalink Gear Review, Gunsmithing 8 Comments »
January 23rd, 2012

SHOT Show: Crosman’s New .177 Air Rifle Upper for AR15s

Crosman unveiled a great new product at SHOT Show — a dedicated upper that transforms your AR-platform gun into a .177-caliber air rifle. Smart idea. Crosman deserves praise — we wish this was on the market decades ago. This is great for service rifle shooters who can now practice at a fraction of the cost of centerfire ammunition. Since the lower is unchanged, and the sights are the same as on a service rifle, the shooter doesn’t have to adapt to a different trigger or sight height/radius.

Crosman mar177

As Crosman representative Mark Deboard explains: “With the [MAR 177 upper kit], you can take off your AR’s centerfire upper, replace it with the Crosman upper and go to your basement or garage to shoot .177 pellets. You’re getting great trigger time without going to the range and without buying .223 ammo. You can buy a tin of 500 pellets for about five bucks.” (With a good pellet trap you could practice in your basement — but first consult your state and municipal regulations).

Crosman MAR 177 air rifle AR15The 7.4-lb Crosman MAR177 Conversion Kit replaces your existing AR/M4 style upper and converts it into a PCP .177-caliber competition air rifle with 21″ free floating Lothar Waltherâ„¢ barrel. Designed to support 10-meter match air rifle competition, the MAR177 is also suited for service rifle shooters who want to practice indoors in winter. Fitted with a 10-shot rotary magazine, all the shooter has to do work the bolt back every time after firing. The air reservoir offers up to 120 shots per fill.

It looks like the Crosman MAR177 will be popular. Crosman’s Deboard noted that: “We took the MAR177 to Camp Perry last summer for the High Power Rifle Championships, shot it inside the 20 foot Crosman Trailer and everyone loved it.”

Price and Availability
The MAR177 starts shipping 1/25/2012. It is available initially at crosman.com, creedmoorsports.com, and pilkguns.com. Look for retail price around $700, though Creedmoor Sports has a pre-order price of $600.

Permalink Competition, New Product 5 Comments »
December 7th, 2010

20 Practical AR Uppers Deliver Great Accuracy

In 2008, as a “proof-of-concept”, AccurateShooter.com created a 20 Practical AR15 “Ultimate Varminter” with a custom 20-caliber upper from Robert Whitley. That project rifle was ultra-accurate — every 5-shot group out of the gun was less than the size of a dime. That gun was auctioned off, but Robert Whitley (AR-X Enterprises, LLC) continues to produce custom 20 Practical AR15 uppers. (The 20 Practical cartridge is simply the .223 Rem necked down to 20 caliber — you can use standard .223 brass and load with standard.223 Rem dies. Just swap in a smaller expander and use smaller neck bushings.)

20 Practical AR uppers

Robert reports that the accuracy of the first 20 Practical AR15 was no fluke. After buildign six (6) more 20 Practical uppers, he tested them for accuracy and they all shot great. These uppers feature DPMS low-pro receivers with side charging handles. They are fitted with PacNor 1:11″ twist, three-groove stainless barrels.

Robert reports: “We have been making more 20 Practical AR15 uppers and I have to say I am astounded by the accuracy of these things. For shooting little tiny groups out of an AR15 with bullets going 3500+ fps, it’s hard to beat the 20 Practical. Today I test-fired six more uppers, all with 11-twist barrels. Three of the uppers had 24″ barrels, two had 20″ barrels, and one had an 18″ barrel (we call it ‘Stubby’).

20 Practical AR uppers

In four of these uppers I shot re-sized Winchester brass using 25.3 grains of WC844 powder with Berger 40gr BTHP bullets loaded at 2.225″ OAL (about .015″ off the lands). WC844 is inexpensive military surplus powder that is nearly identical to H335. I tried three different primers and the choice did not seem to matter (CCI BR4, Rem 7 1/2s and Win Small Rifle — the old silver ones). All these four uppers shot great. Here is an overlay with targets from uppers #6, 10, and 11. All groups are mag-fed, 5-shot groups shot at 100 yards using a front rest and rear bag.”

20 Practical AR uppers

20 PracticalNeck Tension is Important
With four of the uppers, Robert used Winchester brass which had good neck tension, and accuracy was excellent, as shown above. However, for two of the uppers (uppers #3 and #5) Robert used some old 20 Practical ammo that he pulled down and reloaded without re-sizing the case neck. Robert says: “With this old ammo, the neck tension was way too light and the accuracy was so-so, i.e. between .75″-1.0″ at 100 yards — which for a lot of ARs is still considered ‘very good’.” Lesson learned — accuracy may suffer with the 20 Practical if your neck tension is inadequate.

For more information visit www.6mmAR.com, or contact Robert Whitley via email: rcw3 [at] erols.com.

Permalink Hunting/Varminting, New Product No Comments »