Straight Bullets

We’re going to be talking about sending bullets straight into the back of the barrel in this article and how doing so contributes to tight groups. Good bolt-gun builders seem to have understood the importance of this before we gas gunners. If gunsmiths and shooters whose passion is the Stoner platform hope to rival bolt-gun performance, we need to take a few pages from their book. In doing so, both the gunsmith and the shooter share responsibilities. What happens when a bullet hits the back of a barrel off center?

It’s easy to envision the front end of the bullet being deformed and how that will degrade accuracy, however, some might ignore the also-important bullet base. If the front of the bullet is at an angle, the base will be tilted proportionally. That tilt will remain with the bullet as it spins down the bore. Where that tilt becomes critical is in the split second Bullet seated in the cartridge on the bottom is crooked and will be damaged when it impacts with the back of the barrel off center.

Pay attention to how the base of the bullet is also tilted. the bullet exits the muzzle when one side of the bullet is outside of the bore while the opposite side is still in. This will allow gas pressure to escape, causing the bullet to be pushed to the side. This is similar to a damaged crown allowing gas on one side of the bore to escape prematurely and push the bullet off course. In another lifetime, nearly a half century ago, I was a competition pistol shooter and hand cast some of my lead bullets.

I remember other bullet casters who greatly valued a nice flat and straight base. I didn’t fully understand the emphasis on this at the time. Now I do. Gunsmith Preventatives AR gunsmiths can buy barrels with the same quality used by gunsmiths building bolt guns. So if two "identical" barrels come out of a given factory on the same day and one ends up on a gas gun and the other on a bolt action rifle, why does the latter usually shoot tighter groups? We’ll consider receiver squaring first.

Gunsmiths building custom bolt guns sometimes buy quality custom actions that arrive squared. When using lower cost receivers, the diligent gunsmith will perform squaring operations to the receiver face (front). For decades, AR gunsmiths have turned a blind eye to this process. With the exception of some very high-end receivers, like those made by Sun Devil, most AR receivers come from the factory with run out with one side of the receiver face taller than the opposite side.

When the AR gunsmith pushes the barrel extension into the receiver, the raised flange on the extension will contact that high side of the receiver face and stop. As the barrel nut is drawn up and exerting pressure, the barrel will be set at an angle inside the receiver. Since there is so much slop in the fit between the barrel extension and the corresponding inside surfaces of the receiver, there is no resistance to the barrel seating at an angle.

If the bolt carrier assembly is perfectly aligned with the receiver when it delivers a cartridge to a barrel that is set crooked, there is no way that a cartridge attached to the bolt face is going to line up as well as we want with the center of the barrel’s bore. I believe that runout in the receiver face likely influences barrel harmonics as well. As the barrel whips, those high spots constitute a pivot point making shot-to-shot harmonics less uniform.

Those uneven harmonics likely cause the barrel extension to relocate to different angles inside the receiver. The barrel extension becomes a moving target for the bolt to try to align with for

each shot. Most gunsmiths assemble the AR rifle and leave all that slop between the barrel extension and the upper receiver, permitting the extension to move around which causes the muzzle to return to a different position after each shot, resulting in fat groups. The solution is twofold. Start by properly squaring the faces of your receivers. I performed a study on this. I built temporary guns on a bunch of receivers and machine rest tested them with known lots of match ammo.

Then I disassembled each gun, properly squared the receivers, and reassembled each temporary gun using the same parts, torque settings, etc. Using the same Properly done, this will shrink groups by an average of 14%. ammo lots, the squared receivers improved by a significant 14%. Let’s be clear on the squaring procedure. This needs to be done on a lathe. I tried a squaring tool that fits in a hand drill.

Using lapping compound, the long section fits into the receiver and it’s supposed to result in proper alignment of the squaring surface as even, forward pressure is applied to the drill. However, used as recommended, I measured the run out of a receiver was about half again greater than the undoctored first reading. I chucked that tool in the trash. Comparing once again to bolt gunners, they do their receiver face squaring on a lathe and not by running something in the receiver attached to a hand drill.

With the receiver face properly squared we are part way to a solution. Next is to stabilize the extension in the upper receiver. This is best done by matching a BAT Machine custom barrel extension to the upper receiver to achieve a tight fit. You can also use a thin (0.001") sec- Author found using this tool to attempt to square receivers actually makes them worse. tion of shim stock wrapped around the stock extension and held with green Loctite 620.

Properly done, this keeps the barrel extension in one consistent position at the front of the receiver and the muzzle of the barrel will return to the same spot for each shot, cutting group size by about 1/3. This is so important that I wrote about it in, "The Relationship Of Barrel Extension Diameter To Accuracy In The AR-15" (March and April 2013.) Chamber Selection It is generally thought bolt-gun chambers can be tighter than those in gas guns. This is a function issue.

It’s easy to visualize a cartridge in a tight-fitting chamber where the bullet lines up more directly with the center of the bore than the same cartridge in a sloppy chamber. Most AR gunsmiths elect to not use tootight chamber reamers for fear of function issues during feeding. The body of the cartridge case (side walls) offers a lot of surface area which can contribute to friction and drag during both feeding and extraction. Case necks, however, offer much less surface area.

Necks in the .223 Remington are shorter than some other .22 centerfire rounds and can be tightened just a little. The feasibility of this will be dependent on several variables. The first is use. If I know my customer will be only single feeding rounds you can be sure I’m going to use a reamer that produces a tighter neck. Type of brass and how it is processed are important variables.

Lake City and Winchester brass tend to be thinner than WCC and Lapua brass which are needlessly thicker with no positive pay back that I have ever been able to deter-

mine. In addition to thicker brass taking up more space in the chamber neck, it pressures up more, causing handloaders to have to reduce powder charges. Outside neck turning is an option that thins brass at the neck and also has a vote in how you should order your reamer. Work with your reamer maker on dimensions and the specific variables of your project. I get my reamers made by Pacific Tool and Dave Kiff there asks me about these variables when I am working with him on a reamer order.

If your reamer maker isn’t asking you these questions you need to consider switching to a maker that does. However, if you area general gunsmith that only builds a few ARs a year, you will likely elect to just own one reamer. Freebore is another important chamber dimension for straight feeding. This section of the chamber immediately in front of the case mouth is smooth without rifling and about the same diameter as the bullet.

Longer freebore causes more bullet jump needed to make it to the lands when they’re seated to magazine length. Visualize a water hose. The further the water spray is from the hose, the further it is from the center of the nozzle. Accuracy is enhanced by avoiding excessive bullet jump. For those shooting a combination of magazine-length ammo and longer single-fed rounds, I recommend the Wylde chamber. For magazinelength ammo only, I recommend the Compass Lake Engineering chamber.

Guns with excessive freebore, such as 5.56 NATO, "shoot out" earlier. In fairness, freebore length can be used to help control pressure or make room for longer bullets. Work closely with your reamer manufacturer on this dimension. For more information on chambers refer to my three part article, "AR-15 Chamber Selection" (July-September 2014). Leade angle will be our final chamber topic. You need to specify your choice on this when ordering a reamer.

Wylde reamers should come with a leade angle of one degree and 15 minutes but double check with your reamer maker to be sure this is what you are getting. Regardless of reamer and chamber dimensions, you can always specify this gradual leade angle which seems to ease the bullet into the back of the barrel and may result in less bullet damage even when bullets are off center.

In that 2014 series on chamber selection, I lay out specific reasons for concluding that this leade angle treats bullets more gently than more abrupt angles. Match Bolt Carriers Two primary match bolt carriers are from JP Enterprises and Young Manufacturing. Both fit the upper receivers better than regular carriers and have greater polished bearing surfaces resulting in more uniform bolt carrier velocities and lock ups.

I performed an exhaustive study on group sizes of ARs with regular carriers and then substituted match carriers. The groups fired with the match carriers averaged 8.8% tighter than groups with standard carriers. I attribute the improvement in precision to better positioning bullets on the center of the bore. See "AR-15 Upper Quick Fixes: Match Bolt Carriers" (May 2014). When positioned all the way forward, bolt carriers tend to tilt downward at the back causing the bolt face to be set at an angle.

Since the cartridge is attached to the bolt face, it is also thrown out of alignment and causes the bullet to enter the back of the barrel at an angle, deforming it. Gunsmiths have known of this accuracy shortfall since nearly the invention of the AR-15. Early attempts to correct the problem failed and gunsmiths were discouraged and largely ignored the problem for decades.

I picked up the gauntlet and described my efforts to fix this in "Combating AR-15 Bolt Carrier Tilt" (May 2017) and characterized the "baby steps" taken and implored gunsmiths to improve on my work. In that article I described the adjustable anti-tilt pads that I

equip all of my carriers with. This causes carriers to be level inside the receiver and better positions ammo in line with the bore. This results in tightened groups about 14% better than a match carrier without pads. Gas Tube Alignment Very closely related to the previous topic of carrier positioning is the subject of gas tube alignment.

The gas tube should leave the back of the front sight assembly or gas block and touch absolutely nothing until it goes straight through the "cloverleaf" hole in the front of the upper receiver and straight into the carrier key. If the back of the gas tube enters the key at an angle, the whole carrier will be forced out of alignment and, most important, the bolt face will be at an angle.

There is abundant slop in all AR chambers and the fit of the bolt inside the barrel extension results in rounds positioning their bullets off center. This is such an important and often overlooked topic that I have written two articles on it in the March 2014 and May 2018 issues. Twist Rate Don’t over spin bullets. The twist rate of the barrel needs to match the longest bullet that the firearm will be shooting. Longer bullets require faster twist rates.

Once a bullet is stabilized, spinning it even faster doesn’t help at all. Over spinning a less-than-stellar bullet, such as one damaged by entering the bore at an angle, will only make groups fatter. Eric Stecker from Berger Bullets used to have a post on their company website about this topic. Paraphrasing, he said that overspinning exacerbates imperfections in the ammo. If a 1:8 twist will stabilize your 80 grain bullets, don’t use 1:7.

If you don’t know what twist rate to use for a given bullet, many barrel makers and bullet companies make this information readily available. Case Issues We have all picked up brass from firing ranges that exhibited deformed rims. These deformations often take the form of "ripping" the rim to the rear of the casing. Those tears in the rims are often the result of the bolt trying to open but meeting resistance during extraction.

Sometimes those rips in the rims deform the case so bad that you can’t even get it to fit in a shell holder for reloading. Even if you are able to resize around that is cocked in the shell holder, what are the chances the case will come out concentric? Sometimes these boogered casings can be salvaged by simply placing the heads on a flat file and working down the high spots. Maybe some of you will find that too low tech?

The flip side is, what happens when you chamber a deformed round and the bolt face closes on a high spot in the case rim. Obviously that round will end up being cocked in the chamber and will not orient the bullet properly with the bore. What is the best way to deal with torn cartridge rims throwing bullets out of alignment with the bore of the rifle? Don’t bend the rim in the first place! There are any number of possible culprits at work here. The gun owner can address some of them.

A good start may begin at the loading bench by reducing powder charges by a few tenths of a grain, although I must point out that heavy 80 and 90 grain bullets shot out of the .223 Remington perform best when pushed hard. Gun owners are encouraged to use a chamber brush during their

cleaning following each range session. Tumbling cartridge casings during the reloading process will also enhance extraction. Gunsmiths can further this by polishing chambers. I wrote about how to do this in the article I cited previously on chambers. Dwell Time Semiautomatic firearms often extract fired casings easier when timing of the bolt or slide opening happens after most of the chamber pressure has gone down. One way gunsmiths can control dwell time is by the location of the gas port.

All other things being equal, the closer the gas port is located to the chamber, the sooner gas bled from that port will reach the carrier key and begin unlocking the bolt. AR gas tubes are available in various lengths. Depending on the specific project and customer preferences, gunsmiths can use longer tubes to increase dwell time. Gas port sizes vary in relation to where the port is located. Generally speaking, the closer to the chamber, the smaller the port needs to be.

On Match Rifles, I use a two-inch longer gas tube than typical from White Oak Armament. Shooters participating in Long Range competitions tend to use heavy 90 grain bullets pushed fast. The extended gas tube coupled with a gas port about one drill size fatter than normal results in a longer dwell time. With the exception of .22 Nosler, I can’t remember the last time I picked up a case with a torn rim from my test shed floor. Watch for a dedicated article on the pros and cons of the .22 Nosler soon.

Another method of increasing dwell time is to insert a bolt carrier weight in the back of the carrier. These weights look like a shotgun shell and the kit comes with different weights to tailor to specific needs. Dress down the buffer with a file as per the included instructions if the weights are left in place for rapid fire events and leave them in during load development. Reliability, group size, and location can be negatively impacted if this is ignored.

If you can’t find suitable weights, contact me and I can help. Gain Twist Gain twist starts bullet rotation slowly and speeds it up toward the muzzle, lowering pressure and enhancing extraction. With the exception of the .22 Nosler, I never have bent rims on cases fired in gain twist barrels.

Other potential advantages include improved accuracy, longer barrel life, cooler operation, and less rotational torque. "Revisiting Gain Twist" (November-December 2013) and "Gain Twist Barrels For Palma" (December 2016) discusses this further. Ejector Pressure Armchair experts posited for years that a left-mounted ejector and its spring pushes the cartridge into the chamber to the right of center, degrading groups. In a world where thousandths of an inch can have a huge impact, this theory sounds plausible.

Chambers do have several thousandths of an inch of clearance around the loaded round so I understand how guys came up with this theory. I took a little step forward from others, however, and abandoned the easy chair and air conditioning for a hot, dusty test range. I fired groups from a number of uppers and labeled them. Then I completely removed the ejectors from the bolts of each upper and tested a second time with the same lot of ammo. There was no improvement in group size! Lesson learned: Don’t

The Hornady on the far right will actually straighten the round. mess with ejectors. Your groups will not improve and you may compromise function. Shooter Preventatives Let’s move from the gunsmith’s chores to the shooter’s tasks in feeding straight bullets. I mentioned previously to clean the chamber using a chamber brush after each range session. Add to that a thorough cleaning of the bolt carrier assembly and finished with fresh lube. Don’t be afraid to add lube during extended range sessions.

If you shoot events like High Power, Palma, F Class, and other long-range matches where you feed rounds one at a time, I recommend using a Bob Sled magazine. These don’t have a spring-loaded follower, just a trough the cartridge lays in, and eliminates upward pressures on the bottom of the carrier which can vary and push the carrier out of alignment. After you have placed the cartridge in the trough, use the tip of your index finger to push it forward into the chamber.

When your index finger contacts the front of the ejection port, stop and pull your finger out, trip the bolt catch, and fire the round applying the appropriate fundamentals of marksmanship. My tests show that this simple, cost free, and fast technique will result in an average reduction in group size of 13.8% compared to just dropping the round on the top of the magazine and tripping the bolt catch.

I believe this results in more uniform positioning of the cartridge on the bolt face and in the chamber and helps keep straight bullets. Most of the rest of this article will deal with ammunition, both factory and handloaded. I strongly recommend reading "Better Ammunition" (April 2016) before proceeding. If you don’t have a copy, email me. The first topic is cartridge concentricity which has to do with how well the bullet is lined up in the cartridge neck with the centerline of the whole case.

This is measured in thousandths of an inch as run out. Simply stated, bullets in cases with run out are seated crooked and we need to avoid this. There are a couple of ways of dealing with this and both require a tool often referred to as a spinner. Spinners hold rounds in place while the operator rotates (spins) them while a dial indicator pressing against the bullet measures how much run out, if any, there is to a thousandth of an inch. This finds any "high spots" of the cartridge.

Back in the day, we culled out rounds with the most runout for close range practice. Straighter rounds were saved for long range and important matches. This worked fine but a few years back the good folks at Hornady invented a better spinner. Their cartridge straightening tool can also push the bullet into better alignment, is quick and effective once you get the hang of it, and reasonably priced. Culling or straightening works with both factory and handloaded ammo.

As a related point of interest, high-end rimfire shooters use a .22 spinner made by Nielson Brothers Arms. Spinners are also useful to measure runout in some pistol ammo and pistols shoot straight ammo better just as rifles do. I stress to my customers that no gunsmith or barrel maker can produce a firearm that will shoot optimally with crooked ammo. No matter what you do, some ammo will come out of the loading press or arrive from the factory with run out.

However, handloaders can take steps to minimize both the severity and frequency of run out. This begins with die selection, how dies are mounted in the press, and how bullets are seated. I recommend match dies from Redding or Forster. There is a process to mount the dies in the press for better alignment. That process is described in my article, Glen Zediker’s

Handloading For Competition, and on the Sierra Bullets website. During the bullet seating process, I recommend a "half seat and spin." Approximately half seat the bullet, remove the pressure on the ram of the press, spin the round about 180 degrees, then finish seating. Rounds will come out about 0.001" straighter than if you seat in one stroke. Regardless, please don’t slam the ram. This results in poorer concentricity. The thickness of the walls of cartridge casings is far from uniform.

Where this lack of uniformity is most important is the neck. If the thickness of one side of the brass is greater, the thick side will resist bullet seating to a greater degree and cause the bullet to cock in the neck. Likewise, when bullets are fired from such a casing the thick side of the neck will hold on to the bullet harder, sending the bullet into the back of the barrel at an angle. There are a couple of ways to deal with neck thickness problems.

There are gauges that measure neck wall thickness so those with the most uniformity can be reserved for long range and important matches. Outside neck turning aims to make all brass usable by shaving the neck where it is thicker. This is gun specific. Some guns respond very well while others are more neutral. Chamber dimensions have a vote here as tight neck chambers respond better to outside neck turning.

I recommend every gun owner experiment with this is determine if their gun responds favorably or if it doesn’t make a measurable difference. I doubt that there are many handloaders who have access to a lathe but those that do need to read Norman E. Johnson’s very intriguing article, "Precision Case Neck Turning In A Lathe" (May 2018.) We have talked about better centering bullets by using tight neck chambers when plausible, such as single-fed slow fire and techniques to better align bullets in the neck.

But the neck is a small part of the whole case. What about the case body? There is a solution there as well. When around is fired, the case walls swell under tens of thousands of pounds of pressure. The swelling stops when the case walls come in contact with the chamber walls. When that heavy gas pressure subsides, "spring back" occurs. Brass has a sort of memory and spring back causes the walls to return toward their original, non-fired shape by about 0.001".

By no means do the walls shrink all the way back to their pre-fired shape. This small spring back allows the case to be easily pulled out of the chamber during the cycle of function. Such brass is about as close to a perfect hand and glove fit as we can get. We call it fire forming. I recommend picking up those perfectly fire-formed cases, ensuring they aren’t mixed with brass fired in a different gun. For single-fed shooting, neck size only and bump the shoulder back using a special die.

Ammo which is going to be used for magazine-fed events needs to be full-length sized, however. My studies show that fire formed brass that has been neck sized shoots groups 16% tighter than full length sized or new brass. Well worth the effort. Each gun will have a bullet seating sweet spot, which is also the title of an article I published in June 2016. Let’s say that using tips in that article you find your rifle’s bullet seating sweet spot is 0.004" of jump when the barrel is new.

That means that the round is 0.004" shorter than the chamber length as measured by an overall length gauge. Set your match bullet seating die to that length and that sweet spot will remain sweet till the barrel wears. However, we all know that barrel throats erode forward due to the hot cutting gasses developed at the back of the barrel.

That 0.004" of bullet jump may need to be 0.040" after enough shooting and that will depend on how much the firearm is shot, the twist rate, quality of the steel used in the barrel, land height and width, and the burning characteristics of the powder. We can still keep seating bullets at that sweet spot length that we found back when we did our initial load work ups when the barrel was new but that will jump the bullet a longer length before coming into contact with the throat of the barrel.

Like a water hose, however, if bullets are not centered on the bore they will hit the throat a greater distance from center as we jump them further. Smart guys often establish anew bullet seating sweet spot at about the middle of the barrel life, say, around 1,500 rounds. The bullet will be seated further out to compensate for erosion. The longer seated bullet won’t jump as far so the water hose effect will be significantly less. In our example, the initial sweet spot was 0.004".

While we can’t just set the new seating depth to 0.004" of jump and assume it will be sweet but that will be a good starting point to establish the new seating length. Just follow the instructions in my article the same way you did when the barrel was new and you will be fine. Obviously, if you are one of those folks that shoots only magazine-length ammo this technique won’t work. We only use this lengthening method with ammo that is loaded longer than magazine length for hand feeding into the chamber.

I can remember when bolt gunners just turned their heads and snickered when other shooters pulled gas guns out of their cases to participate in precision events. Using the many tips in this article, gas gunners can get their bullets centered on their bores and turn the tables, resulting in the last laugh on bolt gunners. Be one of those gas gunners! Feel free to send me an email to if you have any questions about these topics. Thanks for reading! AG