One shooter asked the forum member: “What makes an AR accurate?” An AR’s parts that can affect accuracy, such as barrels, bolts and bolt carriers, are free-floating handguards, barrels, bolts, bolts, and bolt carriers? He wanted an honest, well-informed response, not sales pitches. Robert Whitley provided a detailed answer to this question based on his experience with AR-platform rifles and testing scores. AR-X Enterprises is Robert’s company, which produces match-grade uppers to suit High Power competitors, tactical shooters and varminters. Robert Whitley: Building an Accurate AR — What’s Most Important
There are many things you can do to improve consistency accuracy with an AR. I use the term “consistent accuracy” because consistency (i.e. Many guns can shoot great 5-shot groups but not great 10- or 20-shot groups. Guns will also shoot differently on different days. Here are 14 things that we believe are crucial to accuracy. 1. Great Barrel: A premium match-grade barrel is a must. It should be well-machined with a great crown and match-type chambering. You must also ensure that the extension threads are cut accurately to the bore. 2. Rigid Upper: An upper receiver with a rigid, heavy-walled structure aids accuracy. The typical AR upper receiver was designed for a lightweight carry rifle. They stripped all metal off it to make it lighter to carry (which is a benefit for the military). Upper receivers are now so thin that you can bend them with your naked hands. These flexible uppers can be used for general purposes, but they are not ideal to ensure accuracy. A rigider upper receiver improves accuracy. 3. True Receiver Face: We have found that truing the receiver’s face is very valuable. This may be controversial, but it is best to keep the barrel and bore in perfect alignment (i.e. barrel extension, bolt, upper receiver, carrier, etc.). 4. Barrel Extension: The barrel extension should be glued or lictitiated into the upper receiver. This will hold it in place from the front to the back of the upper receiver. If there is any play, it hangs on the upper receiver’s face. This is the only source of support for the barrel. 5. Gas Block: A gas block should not put too much stress on the barrel. The clamp-on blocks that grip all the way around the barrel work well. Blocks that are pinned with tapered pins that press against the barrel, or slip-on blocks with set screws that push up directly from underneath the barrel, can cause distortions in the bore of the barrel. 6. Free-Float Handguard: This is a rigid, free-floating handguard (and I emphasize that word rigid) that really makes a big difference. There are many free-float handguards. A free-float guard is an improvement over a nonfree-float setup. However, it is better to have a rigid one. Some are smaller diameter, thin, and/or flexible. If you shoot off any type of rest or bipod, a rigid fore end is best. ARs love to jump, bounce, and twist when they are released. This is because the bullet enters the bore before the carrier begins its cycle. 7. Barrel Contour – You want to have some meat on your barrel. The barrel should not be too thin between the gas block and the upper receiver. We prefer a diameter of 1 inch if it is possible to carry the weight. The gas system instantly starts pressing up with a gas impulse when you touch off a round. This creates vibrations and stress in the barrel, especially between gas block and receiver. This is lowered by a heavier barrel. It is a good idea to keep the barrel contour through the gas block and out to the muzzle a little heavier. ARs have a lot of things going on when you touch off an AR round. The gas system pressures rise and the carrier starts moving (all this before the bullet exits from the bore). Therefore, the heavier the barrel and the barrel contour through the gas block area and out to the muzzle is a good idea. 8. Clearance on Gas Tube Routing: A gas tube should run freely through the barrel nuts, through the front and through the gas key. You must ensure that the gas tube does not get in the way of any of these items so that it doesn’t load the carrier in an unsafe orientation. The gas tube should not be clogged so that it transmits more force and impulse to a barrel when it pressures up than normal. Sometimes we spend a lot time moving the gas block and gas tube around and adjusting gas tubes to ensure proper alignment and clearance. Most gas tubes require some “tweaking” in order to work properly. While factory tubes may work well, they are not designed to be used optimally without being fitted by hand. 9. Gas Port Tuning: It is important to not over-port the gas port. Over-gassing causes the gas system pressure to rise earlier and more aggressively. This can cause more impulse and increase forces and vibration, which can affect the top end as well as the barrel. Adjust the gas port to provide the pressure required to function properly and efficiently, but not more. 10. Front/Back Bolt play: If accuracy is your goal, keep it at.003” and no more than.005 ”).. Factory rifles can have as little as.012′ to.015 play. This is fine if you need to allow for dirt and grime in a military application. This amount of play is not ideal if you want to build an AR with high accuracy. There is a lot of play between the front and back bolts, which allows rounds to be hammered into chambers and then re-formed in a non-consistent manner as they are loaded into chamber. 11. Quality of the component: Only use quality parts from a trusted source. Be wary about “gun show specials”. Every part is different. Some parts are good, others not so good, while some aftermarket parts can be very bad. You don’t have to be afraid to use mil-spec carriers. They are generally excellent for accuracy builds. Remember that just because a carrier has “National Match” or another label, it doesn’t necessarily mean it is better. Chrome-plated parts should be avoided as they can alter the dimensionality of the parts and make it difficult to hand-fit the parts for fit and function. 12. Upper to Lower Fit: It is important to have a good upper/lower fit. An Accu-Wedge in your rear can be used to improve fit. The ultimate solution is to attach the upper to a lower so that they are more like one unit. We try to match the specifications of the upper receivers that we produce with the lowers available. 13. Muzzle Attachments – Don’t mess with the muzzle. You should leave as much metal as possible on the muzzle barrel. Some people like to thread the muzzle to attach a flash hider or suppressor, muzzle brake, and other attachments. But if accuracy is important, you should leave as much metal there as possible. If you have a screw-on attachment, make sure it can be attached and that it stays put without putting too much torque or stress right where the bullet exits. Make sure the barrel’s end is concentric with the bore. Make sure that all muzzle attachments are centered in the bore. This is a common problem with many aftermarket screw-on items. Any gas venting device should vent symmetrically (i.e. If it vents to the left, it should vent equally to the right. And if it vents to the top, it should vent down equally. Inaccurate gas venting can cause problems. 14. Quality ammunition: Ammo can be a whole different story. But loads that are too hot often shoot poorly in an AR-15. Avoid hot loads if you want accuracy from your AR-15. Below are four (4) test groups that were shot with four (4) different uppers with moderate loads. These four uppers had basically the same features as the ones in this article and all shot great. Robert Whitley
www.6mmAR.com
