Accurizing AR-Type Rifles and Carbines, Part 1

Whether you’re a gunsmith taking in a customer’s new AR or constructing your own project rifle, the accurizing of an AR doesn’t have to be farmed out to one of the high-end custom shops. An unmodified or "out-of-the box" AR rifle and carbine in .223 Remington/5.56 NATO will tend to shoot in the 1.5 to 2.5 minute of angle (MOA) range with factory ammunition at 100 yards.

Since 1 MOA equals 1.0472 inches at 100 yards, that means that most outof-the-box ARs will group somewhere between 1-1/2 and 2-1/2 inches at 100 yards. While some shooters relegate these guns to general-purpose duty and will settle for this degree of accuracy, in reality, ARs are capable of sub-MOA accuracy in most common configurations and even 1/2 MOA or better in match configurations.

Of course, a tight-shooting gem can occasionally be had off the rack, but unless the manufacturer built it that way intentionally, finding one is usually a product of blind luck. Until I laid my hands on an accurate AR, I was just as skeptical about their grouping ability as anyone else. I used many different ARs in both 5.56x45mm and .308 Win/7.62×51 while on active duty as a career soldier. Standard-issue guns from the M16 family have never been known as tack drivers, even with match ammunition.

Conversely, those ARs I was issued that had been accurized for special purposes or those built as sniper rifles shot very well, sometimes holding a steady .5-minute of angle with match ammunition at moderate ranges and subto 1 MOA at extreme-for-caliber distances. Tool Time A gunsmith with a few basic specialty tools can easily fine tune these very versatile and popular long arms.

First of all, a bench-mounted vise is a must, coupled with an upper receiver block used to hold the upper firmly while all manner of services are performed. The next item is a lower-receiver block, which locks into the magazine well. This stabilizes the lower so you can do things like changing the trigger, receiver extension, or pistol grip without needing a third hand.

An old, unserviceable 20- or 30-round magazine will also work reasonably well for this purpose; just be sure it’s no good before placing it in a vise. It’s important to get the right size upper and lower receiver blocks for large AR10-sized or small AR15-sized platforms. A good barrel-nut wrench is also indispensable, and these are largeor small-receiver specific. Since each type has its pros and cons, I own several barrel-nut wrenches.

All can be attached to a 3/8-inch-drive torque wrench, which is helpful for setting Assembled lowers lock into the block using the magazine release, whereas stripped lowers like this rely on friction to stay in place.

the proper torque on barrel nuts, muzzle brakes, and optics mounts. I have several because I’m constantly switching barrels and parts, but one good torque wrench will suffice for someone interested in accurizing only a rifle or two. Some combination barrel-nut wrenches will also work on flash suppressors/muzzle brakes and free-float tube-lock rings as well. Lastly, a brass, polymer, or rawhide hammer and an assortment of punches—roll pin, steel, brass and nylon—will make life easier.

Having some extra 1/16-inch punches on hand is a good idea. As I’ve gone further down the custom-AR road, I’ve bought or made additional specialized tools for different accouterments and functions, but they’re generally unnecessary for accurizing just one gun. Instructional resources for constructing ARs from scratch can be found on the web at and Both sites are comprehensive, so I’m not going to get into the basics of AR building here.

Rather, I’ll cover a few simple steps specifically geared towards making an AR shoot more accurately. The stock AR configuration has several accuracy weak points that can be addressed without making drastic structural changes. These will all be covered in this multi-part series of articles, starting in this installment with trigger replacement.

It’s All In the Pull While stock triggers are designed to provide reliable sear engagement and adequate hammer-fall force to ensure primer ignition, this comes at the cost of a light pull and a clean break. While it’s possible to clean up the engagement surfaces of a stock trigger assembly to gain a slight reduction in creep, in my opinion, the effort required to do it safely is much greater than the resulting benefit.

Fortunately, there are a large number of aftermarket triggers available for drop-in, ranging in price from less than $100 to almost $300. The installation procedure is essentially the same for all of these, except that the setup for some is more elaborate than for others.

Always re- Above left and Geissele Automatics’ two-stage Hi Speed National Match (left) and JP Enterprises’ single-stage Fire Control trigger (right, shown with stock hammer) are near the top of their respective games. fer to the manufacturers’ instructions for each trigger type. I’ve installed several makes of twostage match triggers, but my customers seem to prefer those from Geissele Automatics over all the others.

These very well-made trigger assemblies provide three adjustments: first-stage weight, second-stage weight, and overtravel. Some other brands allow for adjustment, often through the use of replacement springs. Geissele’s triggers have individual hex-key adjustments, and if you follow their instructions, they’re easy to set up. For single-stage triggers, I’ve had the best luck with JP Enterprises trigger assemblies. These are highquality units with some adjustability and a range of weights to choose from.

While the Geissele triggers all come standard with anew hammer, JP gives the buyer the option of purchasing the trigger unit only and using the stock hammer, or buying their "Speed Hammer," too. To install anew trigger once you’ve ensured the rifle is unloaded and cleared, remove the upper receiver and set it aside. It helps to have a lower-receiver block to hold the lower in a vise while performing the next steps.

Remove the pistol grip using either the appropriate hex or slotted driver, taking care not to lose the selector-pin spring (inserted into the blind hole drilled in the top edge of the grip) or selector pin, which will fall free from the bottom side of the lower receiver once the grip and spring are removed. You’ll save time later if you remove the safety selector at this point. To do so, the hammer should be in the cocked position with the selector in the "fire" position.

With one hand, push the hammer to its full-down position (past any engagement points), which will allow the selector to slide out from right to left. While controlling the hammer (or with the aid of a dry-fire block inserted in the magazine well), pull the trigger to release the sear engagement and allow the hammer to travel forward, thus preventing it from slamming against the receiver wall. Next, use a dummy pin or punch to carefully drive the hammer pin out. There are two common hammerand trigger-pin sizes.

Most manufacturers are now using .154-inch pins, but late-model Colts and some others use .172-inch pins. On stock units, the hammer pin will go out in either direction. It helps to place a hand on the

opposite side to receive it as it comes out. With the dummy pin or punch still in place, grasp the hammer and apply a slight pressure to contain the spring tension as you remove the dummy pin or punch. Then carefully remove the hammer assembly and set it and the hammer pin aside. Repeat the process of pin removal on the trigger pin.

After the trigger pin is out and the punch has been withdrawn, you can ease the trigger assembly out by pushing up on the trigger from the bottom with one hand and removing the unit with the other.

The trigger is under somewhat less spring tension than the hammer, but care must be taken on stock units to retain the disconnector and spring, which will be loose Removing too much metal will result in a safety malfunction and an unsafe gun, so file in small increments and test fit periodically. once the trigger pin is removed. Generally speaking, the installation of the new trigger is simply a reversal of the removal process.

Nevertheless, if you’re not familiar with the process, paying attention to the orientation of the hammer and trigger springs as they came out will help you when it comes time for the new ones to go in. Both will be under tension when fully aligned with their respective pin holes. Normally the toughest part is aligning the trigger, disconnector, and lower receiver holes at the same time, as both trigger and disconnector are under separate tensions.

Some designs— Geissele’s, for example—are easier to install than stock triggers. Adjustments vary by manufacturers, so the ability to follow instructions (or the willingness to call customer service) can be useful. Often, in order for the safety selector to function properly, some metal must be removed from the slotted portion of the selector lever’s underbody. Some trigger designs also allow fitting by filing the tang that extends under the safety. Regardless, file slowly, evenly, and a little at a time.

It’s much better to remove a small amount of metal (continued on page 14) and go to the trouble of test fitting repeatedly (which requires installation and removal of the trigger assembly each time) than to buy anew premium trigger. Once the safety selector, trigger, and hammer function as designed, the selector pin, spring, and pistol grip can be reinstalled. A small dab of high-lubricity oil on the tip of the selector pin before it’s installed will keep the safety functioning smoothly.

Ensure that the selector-detent spring’s hole and the corresponding hole in the lower receiver line up correctly. If the spring is pinched off through misalignment, it can reduce tension on the selector and allow the safety to be taken off too easily. After completing the reassembly, check the sear engagement using the trigger manufacturer’s instructions. Ensure that the engagement is adequate for safe operation.

Finally, assemble the upper and lower receiver together and perform a function check using the following steps: 1. Point the rifle in a safe direction and make certain it’s clear. Do this by ensuring there’s no magazine inserted in the magazine well, and then retracting the charging handle and checking to ensure the chamber is empty. 2.

Charge the rifle by pulling the charging handle fully to the rear and controlling its forward movement until it’s fully forward and into battery. (Never allow the bolt to slam shut on an empty chamber.) 3. Place the safety selector on "safe" and attempt to pull the trigger. The hammer should not fall, and trigger movement should be slight or nonexistent. 4. Place the safety on "fire" and pull the trigger. The hammer should fall. Do not release the trigger. 5.

While holding the trigger to the rear, cycle the action fully using the charging handle. 6. Release the trigger. The sear should reset with a distinct "click." 7. Pull the trigger again, and the hammer should fall. Repeat steps 4 through 6 several

times, cycling multiple times after each trigger pull to ensure the rifle is functioning in semi-auto mode only. If at any time the hammer rides the bolt carrier forward—indicated by no reset of disconnector when the trigger is released after cycling the action and no hammer fall when pulling the trigger again—the rifle is operating as if fully automatic. Do not attempt to fire the rifle in this condition, as the sear engagement is not properly set.

Repeat the adjustments as per the manufacturer’s instructions as necessary until proper sear engagement is attained and the rifle passes the function check. Conclusions/Recommendations Once the new trigger is installed and passes the function check, a trip to the range with some known-quality ammunition will tell the tale of improvement. Hopefully, you’ve pretested the AR with this same lot of ammunition, so you can make a proper before-andafter comparison.

While firing, keep an eye on the hammer and trigger pins to ensure they don’t drift out. If they do, you either need to replace them with over-sized pins (Geissele Automatics includes them with all commercial triggers) or use captive pins, designed to stay in place. Of all the accurization techniques possible with the AR-type rifle, installing a good trigger is probably the best first step.

Though a noticeable decrease in group size should be observed, other steps are still necessary to bring the AR up to its full accuracy potential. In Part 2 next month, I’ll cover a method for free-floating the barrel and lapping the upper receiver, both of which can greatly enhance the rifle’s performance. ■