Better Ammunition

I was disappointed when I accepted the position of Armorer for the Army Reserve Shooting Team and machine-rest tested all 135 of the Team’s match AR-15 Service Rifle uppers. I found only 39 would shoot 10 shot groups of minute of angle using Team-issue match ammo. That was unacceptable and it took an enormous amount of work to correct. I had to not only rebuild the guns but make the ammo "more better" as well.

When I left the team I had cut average group sizes fully in half and every one of those 135 uppers would shoot sub-minute machine rest groups. While our focus usually isn’t on ammunition and reloading, we want our customers to be happy with the guns we build for them. None of us can build guns accurate enough to compensate for bad ammo. Concentricity and management of run out is cheap and effective. It also works The Porter’s Precision tool (left) and Hornady model (right) also straightens our rifle cartridges.

Below center: Graphic by ISM Services. Notice how the base of the top bullet, seated straight in the casing, will be perpendicular to the axis of the bore while the base of the crooked seated bullet (bottom) is tilted at an angle.. on factory and hand loads, rim fire and centerfire ammunition for rifles and pistols.

Gun Tec Dictionary defines bullet run out as, "The measurement (usually in thousandths of an inch) that a bullet and/or case are misaligned in relation to the centerline or axis of the entire case." Our Team was dealing with concentricity since the 1980s. We didn’t have the options available then as we were competing with M14s and issued Lake City M852 .308 ammo. I still remember waiting in long lines before daybreak to receive ammo. We then brought it to the Assembly Line and "spun" it on a concentricity gauge.

The least straight cartridges were used for standing, better stuff for 200 and 300 yard rapid fire, and the best saved for 600 yard slow fire. How does concentricity influence accuracy? First, boogering the bullet. Imagine the bullet slamming into the back of the barrel off center. That bullet is going to be deformed and never fly true. The poorer the concentricity and the further the bullet travels before entering the rifling, the greater the deformation damage with most of it at the front of the bullet.

Another issue is cocking the base of the bullet. For maximum accuracy, the base of the bullet needs to be perpendicular to the bore. During the instant a bullet exits not perpendicular to the bore, gas pushes unevenly and tips it slightly off center. Nonconcentric ammo will bullet bases arranged randomly and any given round may tip in differing directions, opening the group and causing fliers. Poor quality control in bullet manufacture can cause non-squared bullet bases, though match bullets are high quality.

Crooked seating is a bigger concern. The mirror image of a bullet base cocked at an angle is a barrel crown machined less than perfect or damaged. This also causes gas pushing unevenly on the base of the bullet at the instant of exit and tilting the bullet slightly off course. I was not aware of any cartridge straightening tools in the 1980s so we sorted them. Today, there are tools that can straighten crooked ammo. Porter’s Precision and Hornady make two examples.

Ammo with run out that is straightened seems to shoot

22 LR concentricity gauge from Nielson Brothers Arms. Culling or straightening reduces the problem but the best cure for bullet run out is to not have any in the first place. When loading ammunition take steps to produce the most concentric cartridges possible. Start with competition bullet seating dies, such as from Redding or Forster. They have a spring-loaded sleeve as well as ammo made straight.

If I start with a factory-made cartridge with six tick marks of run out and I straighten it to only two, ten-round groups will normally be as good as the same cartridge that originally measured two tick marks without correction. I do recommend avoiding ammo that is over corrected for match use. If I get too heavy on the straightening tool and push the run out too far the other way, even if finally corrected I’ll just use that round for standing practice.

Long range ammo seems to shoot better with light neck tension. Go too light and bullets can become loose in the case necks after straightening so I recommend just a little more neck tension (0.0015") to avoid this. All things being equal, older guns that have longer throats due to erosion require a higher standard of concentricity control than shorter throated guns.

The further a bullet travels before engaging the rifling the further from the center line of the bore it hits and has developed more speed so it is hitting harder and deforming worse. Quantifying Improvements Concentric ammo shoots better in any rifle and handguns. Ransom Rest testing of handguns shows improved performance with concentric ammunition of a similar degree to rifles.

Rimfires also benefit from having their ammo spun and Nielson Brothers Arms (Nielson- Brothers Arms. com, from crooked ammo by selecting or straightening cartridges to 0.003" of run out or less. For 1000 yard events, the standard is 0.002" or less. manufactures a rimfire gauge and have calculated that for every 0.001" less run out, group sizes improve about 0.2" at 100 meters on average. I’ve machine rested AR-15s with similar results.

The most common cause of fliers is shooter error, followed by improper gun maintenance, changes in conditions (wind or lighting changes), and poor ammo. Eliminate fliers Top: AR-15 machine rest test at 100 yards. Note how group sizes tighten and the severity of fliers is decreased as concentricity becomes better from top left through the bottom groups. At top is a horrible group from ammo with 0.005- 0.006" of run out. To the right, the same gun and ammo but with an average run out of 0.0041".

At the bottom is a one-inch group with 0.002-.003" of run out. A fairly typical difference. Bottom: It took only minutes to sorta box of ammo to achieve the bottom group. The rifle was thought to be "shot out" due to poor 300 yard scores. The shooter was spinning 600 yard ammo only. The throat measured a 0.25" jump with magazine-length 77 grain ammunition, where brand new Wylde chambers jump the same ammo 0.090". Ten randomly-selected rounds produced the top group.

Spinning the remaining 40 rounds from the same box revealed a particularly crooked lot of ammo and I had to accept run out up to 0.004" but more consistent concentricity produced the group at bottom. Ideally, select or straighten ammo to 0.003" of run out or less, and 0.002" or less for 1000 yard events.

at the bottom that keeps the bullet in better alignment with the case neck. Micrometer adjustment to vary seating depth is worthwhile. Other factors in the press will conspire to determine concentricity, such as the shell holder and the alignment of the ram to the die. Glen Zediker’s Handloading For Competition and Sierra’s web site includes tips for improving standard tools.

To help get your dies properly aligned with the shell holder and ram of your press, follow the die maker’s instructions on how far down to screw sizing and bullet seating dies to the shell holder. With most dies I have worked with there will be a gap between the top of the shell holder and the bottom of the die. Before tightening down the lock ring to capture that setting, place a washer between the top of the shell holder and the bottom of the die. I like to use crush washers.

Apply upward pressure on the press handle to sandwich the washer between the top of the shell holder and the bottom of the die. Hold that pressure and screw the lock ring down securely. Remove the washer and you are ready to load. The Marine Team uses a "half seat and spin" technique and I’ve found it improves concentricity by about 0.001" in multiple die and press configurations. Run the casing with the bullet set on top as straight as possible up into the die and approximately half seat the bullet.

Back the casing off just enough to remove all pressure from it and spin the whole cartridge about 180 degrees, then run it back up and gently seat the bullet completely. Don’t slam the press handle as rough seating adds Author prefers unit on right. Below center: Raise the ram up until the bottom of the die is firmly in touch with the crush washer and hold firm pressure with the press handle while simultaneously tightening the die lock washer. run out regardless of equipment used.

The theory of this technique is the stack up of manufacturing tolerances adds up to misalignment. If there is a "high spot" on one side, spinning the round half way around counter balances any imperfection the opposite direction. Try loading ten rounds by just straight seating in one step and measure for average run out, then load a second set of ten rounds using the "half seat and spin" and measure them. I’ll bet the second ten rounds have less run out.

Back in the M14 days there was a popular rumor that it made no sense to manage your rapid fire ammo concentricity because, "The violence of being fed up out of a magazine and into the chamber would just knock the bullets out of alignment anyway." Being the skeptic that I am, I tested the theory. I spun 10 rounds of .308 ammo and recorded the readings. Using a Team National Match M14, I charged them in a magazine and hand cycled them as violently as I could.

Measuring them all a second time showed not so much as a 0.001" difference in all ten rounds combined. I dug out another magazine and repeated the trial. Again, no difference! I spent the whole morning going through different gun and magazine combinations and by lunch time I still hadn’t induced so much as a lousy 0.001" of additional

Author prefers a hand trimmer to motorized units which seem to induce chatter. Above center: Mark index with a Sharpie on the high side of the cartridge. run out. Fast forward a couple of decades when I was beating up the USAR Shooting Team about concentricity management, I heard the same story applied to the AR-15. I repeated the experiment with the Mouse Gun and arrived at the exact same result. I challenged skeptics to repeat my test and nobody has ever come back quoting that tired myth since.

To be on the safe side, always run between 0.002-0.003" of neck tension on rapid fire ammunition. Sorting And Correcting Handloaders seem to just love sorting things. They weigh brass and bullets, measure bullet ogive, and spend countless hours sorting this and that. Most of it doesn’t help accuracy in gas guns at all. The one exception to this rule is neck sorting. The wall thickness of cartridge casings is not uniform and there are tools to gauge the thickness of case necks.

I have tediously measured tens of thousands of them and have found neck thickness variations often to be 0.005-0.006" in the same case. Even using the best bullet seating die in the world, the thick side of the neck resists insertion of the bullet more, resulting in run out. I have marked the thick side of necks and then seated bullets finding that is a reliable indicator of the "high spot" run out occurs. Variation in neck thickness doesn’t end with run out in the loaded round.

When such a cartridge is fired the thick side of the neck is going to hold onto the bullet with greater tenacity and the bullet is going to tip as it moves forward toward the rifling of the barrel. You have a bullet seated crooked going further off course as it moves out of the neck when fired. Don’t confuse consistency of neck wall thickness with neck concentricity. The latter can also be measured and sorted and using casings with less neck run out will result in more concentric ammo that shoots better.

Brand new factory brass often has necks that are misaligned with the case body. Running crooked casings through dies only removes a small portion of the misalignment. The best way to straighten such casings is to fire form them in a match rifle chamber. The tens of thousands of pounds of pressure generated upon firing do a far better job than any sizing die. Keeping such cases segregated by the firearm they were shot in and then just neck sizing them results in enhanced accuracy.

To date, I’ve found Winchester .223 Remington cases to be the most consistently concentric with the case body. Some corrective measures for uneven case neck thickness. First, use a gauge to select the cases made with little variance to prevent the problem. This measurement takes along time so save those cases for important long range matches. Furthermore, the percentage of casings born good is very limited. I haven’t kept any official tallies but it is entirely possible to gauge ten casings to find a good one.

I like to see necks with no more than 0.001" of variance for long range matches and no more than 0.002" variance for 600 yards. I find consistent necks improves average concentricity by about 0.001". Brass born with good necks and bullets seated in competition dies with good technique often results in loaded ammo with almost zero run out. The second alternative to dealing with varying neck thickness is outside neck turning. Unfortunately, like gauging necks, it is very time consuming.

Hand tools do a good job and attempting to motorize things often reduces consistency. Done improperly, this can decrease accuracy. Outside neck turning is accomplished by running a hardened mandrel down the case neck to round it out and push out imperfections and high spots to be shaved off by a cutter. Properly done, about half of the outside of the neck is touched by the cutter and shaved down.

Any greater cut than that thins the neck excessively, resulting in bullet retention issues, split necks upon firing, gas leakage, and other problems. Note, I’m not saying to cut down the neck thickness by 50%, only that about

half the neck will be touched by the cutter. As always follow the manufacturer’s instructions and check out pages 92-104 of Zediker’s Handloading For Competition. Because the thick sections of the neck have been shaved down, the neck has more uniform thickness, allows more consistent bullet seating and concentricity. When the round is fired the neck releases the bullet evenly on all sides and it tends to enter the rifling straighter. I’ve found neck turning reduces average group size by 21%.

Hand neck turning is slow, so I bought a motorized trimming tool originally designed to trim casings to a uniform length and modified by the manufacturer to perform outside neck uniforming. I have fooled with this thing for years and can’t get it to work right and believe the motor is turning too fast and causing chatter, degrading performance. Even if I could get it to work properly it still isn’t fast. Guns are finicky concerning neckturned brass. Some guns respond very well while others don’t.

I suspect that the neck dimensions in individual chambers may be responsible for some of this, so test each gun with turned and non-turned brass to let the gun’s actual performance tell you whether or not to bother. Another sorting technique is the mark index method. With no straightening tools available, we used to use this to deal with run out. After spinning a cartridge, the high side is marked so that it can be hand fed into the chamber indexed the same way, such as always feed the mark at 12 o’clock.

With the top open in bolt action and M14 rifles, this is easy to do even while in a sling and shooting coat. My experiments have demonstrated this works as my groups tightened up while allowing use of all issue ammunition rather than a portion via the cull method. Years later, I began working with a machine rest and formally tested this. Even ammo with lots of run out shot well if uniformly indexed. AR-15 shooters find this technique more cumbersome due to the rifle’s design, especially when strapped in position.

To make this work, some shooters place a spun and marked cartridge into a stripper clip to feed the round into the chamber through the ejection port. The index mark stayed at 12 o’clock where wanted and the rim of the cartridge even with the leading edge of the ejection port, resulting in more consistent positioning of the round in the chamber and equal pressures on the rim of the casing by the bolt face, ejector, and extractor.

My studies show that employing this technique will result in an average accuracy improvement of 13.8%. To understand how the mark index method works, consider how the base of the bullet contributes to performance. The bases of bullets seated with run out will not be perpendicular to the axis of the bore, causing tipping upon exit. If not indexed, one bullet may be pushed towards 6 o’clock while another at 12, 9, or 3 o’clock, or anywhere in between.

Mark indexing uniforms this by having any run out error in the same direction. Those bullets have no choice but to follow the rifling and will exit with the low side of their bases at the same position and blown a bit off course the same direction. There are two potential limitations to the Mark Index Method. Upon firing, deformation of the front of the crooked bullets will still occur when they slam into the back of the barrel off center.

While the method evidently causes the bases of all bullets to index uniformly relative to their exit from the muzzle, it doesn’t correct the amount of bullet tipping and 0.006" of run out will exhibit more error than 0.002" even if it’s in the same direction. Mark index, when coupled with either straightening or culling rounds, can be extremely effective, especially with open top actions. The rifle machine rest I use shoots groups about half the size as High Masters normally deliver off the shoulder.

Even with that kind of performance I never fire around without using mark index. Mark index works far better than it "should". My studies show it reduces group size by 17.6% on average. While not quite as effective as selecting ammo born straight or using one of the straightening tools, it is faster than straightening.

Mirror Image The mirror image of cartridge concentricity is positioning cartridges uniformly in the chamber each time and always striving to get the bullet lined up perfectly with the center of the bore. A whole lot easier said than done! In my articles "AR-15 Chamber Selection" in the July-September 2014 issues, I discussed tight neck chambers. These certainly help align the case neck and bullet with the center axis of the bore, especially when using neck-turned brass.

However, self-loading rifles need standard dimension chambers for

reliable function. They can be fed with single rounds, however. One of my team shooters reported he saw less standard deviation in velocities when single feeding rounds into the chamber compared to just laying them on the magazine follower and allowing the bolt carrier to shove them in. He wondered if increases in accuracy might also result. I set up a study and found that average group size shrunk by 13.8% if the round was shoved into the chamber by hand.

I theorize this results in more uniform positioning of the cartridge in the chamber. My May 2014 article "AR-15 Upper Quick Fixes: Match Bolt Carriers" discussed match bolt carrier potentially offering improved accuracy by an average of 8.8%. I believe this is attributable to improved consistency in positioning of the round in the chamber. Until the problem of AR-15 bolt carrier tilt is corrected, the bolt face won’t line up perpendicular to the bore and cartridges will always be somewhat out of alignment.

More uniform positioning occurs with fire forming after neck sizing. Shooters in the long range community have been employing these techniques for years to wring improved accuracy with their bolt guns. My tests show improvements with Stoner platforms if properly applied. When a gun is fired the casing swells under pressure of the expanding gas. The case walls are forced into tight contact with the chamber walls. When the pressure subsides the case shrinks back about 0.001".

The case never shrinks back to its original dimensions. When the shooter processes the case for its next use there is no need to resize the body because it already a nearly perfectly fit. All that is needed is to size the neck back just enough to grip the bullet. I recommend a 0.247 outside neck bushing with military brass in the AR-15 for slow fire and a 0.246 bushing if reloading neck-turned brass. You also need to "bump" the shoulder back about 0.003".

This calls for a special die instead of a normal full length sizing die. I recommend Forster’s Bushing Bump Neck Sizing Dies and Hornady’s Headspace Gauge attached to a caliper to adjust the die properly. I performed a study on using fire forming followed by neck sizing and groups shrunk by about 16% compared to brand new brass. Fire formed brass is a reloading technique for long range single fire stages, not magazine-fed rapid fire events.

That said, I have fired tens of thousands of neck-sized rounds in magazine-fed rapid fire practice with never so much as a single function glitch attributed to the ammo. It results in ammo that better fits the chamber and aligns bullets near to the center axis of the bore. While working on this article I measured fired brass and compared it to full-length sized brass. The latter exhibited 0.003-0.007" more slop in the case body.

How many of you machinists would be satisfied in locating your chamber with that same degree of error from the center line of the bore? Using full-length sized brass for slow fire events is just the other side of the coin from a misaligned chamber. Don’t mix brass fire formed in different guns because this can jam things up function wise. With afire-formed and neck-sized case body 0.003-0.007" fatter than full-length sized brass, chamber pressures may drop a bit.

If Far you are working right on the edge of primer retention, this can help. Wildcatters may fire form by shooting rounds into the dirt, but realize every round fired is fire formed. Simply pick cases up and used them in the same chamber. Clean chambers also improve consistency. We can hardly expect to center cartridges on the bore if the chamber is full of crud.

Likewise, if we are not cleaning and lubing our bolt carrier assemblies after every range session we can hardly expect them to position rounds uniformly each time with equal pressures on the case rims. I also like to see a little oil going on the rings during range sessions to keep the bolt carrier velocity uniform. Conclusion Getting rounds to line up with the bore starts with the gunsmith selecting a chamber with the right dimensions to match the customer’s shooting needs and brass treatments.

When building new guns I always recommend using a match bolt carrier. Then the onus shifts to the shooter. Spin all ammo and either cull or straightening rounds with excessive run out. Consider the mark index for consistency. If hand loading, either gauge and selecting uniform necks or outside turn them. Consider fireformed and neck-sized brass for slow fire events. Use competition dies and half seat and spin when seating bullets. Always seat slow fire rounds up into the chamber by hand for uniform positioning.

Keep the gun clean and well oiled. Most important, pay attention to conditions and always maintain a religious application of marksmanship fundamentals! AG