Encyclopedic Error

Google doesn’t offer a "book definition" and I don’t claim to have coined the phrase, but I define "encyclopedic error" as an explanation that seems sensible and is accepted as true because it’s repeated often but isn’t actually tested and doesn’t hold up to scientific scrutiny. While I’ve included examples of encyclopedic error as subtopics in previous articles, I have enough examples for an entire article. Some examples of encyclopedic error have flourished for decades, largely unchallenged.

Cartridge Concentricity Cartridge concentricity is important and I dedicated an article to it ("Better Ammunition", April 2016.) Concentricity is alignment of the bullet to the center axis of the case. If not done right, no firearm will perform to its accuracy potential. When I started with the Army Reserve Shooting Team in the 1980s, shooters were "spinning" (measuring concentricity) long range ammunition but not for 200 and 300 yard rapid-fire events.

It was thought that the violence of feeding from a The more modern Hornady Lock-N-Load Ammo Concentricity Tool on the right will both identify run out and correct it. magazine during normal operation, instead of slow-fire hand feeding, deformed ammunition enough to make concentricity management a waste of time. Like all encyclopedic error, it seems logical, especially for people not willing to measure and test things. Something caused my skepticism, so I set up a little test.

I selected ten rounds of .308 factory match ammo, spun them, and recorded their concentricity measurements. Charging them into a M14 magazine, I cycled all ten using the operating rod as violently as possible. Spinning the test rounds a second time indicated no change, not even a 0.001" difference! I repeated the test with several other rifles and magazines and never measured a concentricity change. From then on, I managed concentricity at all yard lines and my scores went up.

Fast forward a decade later when I was the team’s Armorer and we were shooting AR-15s. That encyclopedic error about magazine-fed bullets knocked out of alignment still had not died. To be thorough, I repeated my test with AR-15s with the same results. Those managing their concentricity saw scores improve at all yard lines over those that didn’t. This assumes an AR-15 as Stoner designed it with a 20" barrel, appropriate gas port and gas tube, and internal piston (direct impingement) operation.

It’s important for the upper and lower to align to prevent damage to ammo. Older (more than two decades ago) components didn’t align well, especially in parts guns assembled with unmatched components by non-gunsmiths. Quality control from different manufacturers and foundries has greatly improved so mixing different brands of upper and lower receivers is not nearly the kiss of death it once was.

Also assumed is that magazines are clean, properly adjusted, and the internals (spring and follower) are of modern design and not fatigued or worn out. See "The Art And Science Of Magazine Maintenance" by George Harris in the March 2014 issue. Gas Ports Gas ports in standard 20" AR-15 barrels are drilled about two-thirds of the way down the barrel.

People, I assume that don’t own chronographs, continue to claim that a gas port drilled about seven inches from the muzzle robs enough gas pressure to effect muzzle velocity. With light beer in hand and feet propped up in an easy chair, they pontificate bolt guns with 20" barrels will have faster muzzle velocities. I installed a JP Enterprises adjustable gas block to test this. With a state-of-the-art Oehler chrono-

graph I measured velocities with the gas block wide open and with it completely closed. Despite using known-quality ammunition from the same lot and testing in consistent lighting conditions, there was no increase in muzzle velocity with the gas block shut off. I repeated this test with a 26" barrel on a Match Rifle and had the same results. Derrick Martin, owner of the custom gun shop Accuracy Speaks and author of The Complete Guide To AR-15 Accuracy conducted a similar test with the same results.

More encyclopedic error debunked! Jump Proof Bullets High Power competitors shooting the Service Rifle division in sanctioned National Rifle Association and/or Civilian Marksmanship Program events usually employ two bullet types. The closer 200 and 300 yard stages requires magazine-length (about 2.25") ammunition, commonly a 77 grain bullet or similar. For long range stages (600 and 1,000 yards) they switch to longer and more wind resistant 80 or 90 grain bullets seated closer to the chamber’s throat.

The common Wylde chamber needs a Cartridge Overall Length (COL) of about 2.475" with 80s and about 2.50" with the longer 90s. Despite the differences, some jumped to the conclusion that 77 grain bullets are jump proof, despite the sizeable distance. However, these bullets are nearly unsupported during this travel and can enter the throat at an angle to the center line of the bore, becoming deformed. This jump measures about 0.090" in Wylde chambers, a veritable football field for a bullet!

Every fired round erodes the throat forward, increasing jump and usually decreasing accuracy, though the amounts are quite variable. Far Most Wylde chambers have an accurate service life from 2,000-4,000 rounds. By the time most barrel throats have eroded enough that 77 grain bullets are jumping about 0.25", groups have inevitably worsened enough to demand rebarreling. Fire cracking and roughness from erosion also degrade accuracy.

Hand-fed cartridges with heavier bullets can be longer and seated closer to the throat, reducing jump. Smart hombres can periodically lengthen their long range ammunition to compensate for throat erosion. Thus, a rifle that is "shot out" for 300 yard rapid fire can still perform well at 600 yards. This is a little counter intuitive as shooters tend to expect long range performance to be the predictor of barrel wear. National Match Course tournaments are won by the aggregate of all yard lines, not just at 600 yards.

I frequently remind customers to assess both 300 and 600 yard performance in determining when to rebarrel. So, shooters can be confused where to watch for signs of degraded performance. Throw in encyclopedic error and the waters are muddied further. Here, the claim is 77 grain bullets are somewhat "jump proof" and the increased distance doesn’t effect performance. Testing and observation proves that 77s are better described as "jump resistant." Jumped too far and performance degrades.

Magazine-length 77s aren’t the only types susceptible to this. Military issue 55 and 62 grain loads are also degraded by jump. In fact, my first research about bullet jump centered on military applications. I was a competitor with the Army Reserve Shooting Team in

Far This picture illustrates how far the lighter bullet is jumping which negatively impacts accuracy. the 1980s and we often competed against foreign military teams in Service Conditions matches using issue M16-series rifles and ball ammo. M16s have NATO chambers designed for reliable function in dirty battlefield conditions, sloppy in all dimensions with more freebore than civilian chambers. This causes along jump, seriously degrading accuracy.

I began to experiment with shorter chambers and groups tightened considerably (see "Improving Rack- Grade AR-15s", December 2014.) I wasn’t the only researcher doing this. Derrick Martin, then with the All Guard Shooting Team, was as well. Because we were competing on 01 grain was used to prove there is no relationship between brass weight and velocity of Lake City brass in 20" and 26" AR-15 barrels. different teams then, I didn ’ t know of his re search or conclu sions at the time.

Reading his book I found we conducted similar tests and conclusions on this and other topics. Like me, he found that accuracy with military ammunition was enhanced with shorter freebores. Later, as the USAR Armorer I remembered those chamber experiments and conducted another study. I had 34 new eight twist barrel blanks from two respected makers intended for shooting 77 and 80 grain bullets due for processing by Frank White at Compass Lake Engineering.

I had Frank chamber half of each brand with his shorter CLE chamber and the others with Wylde chambers. I then built temporary guns around the 17 barrels with CLE chambers, broke them in with a noninvasive process, and machine rest tested them with known lots of magazine-length ammo. When finished, I cleaned everything up, tore the guns apart, and reassembled with Wylde-chambered barrels. Same receivers, float tubes, components, torque specs, ammunition lot, everything!

When the gun smoke cleared, the shorter CLE spanked the longer Wylde by a substantial 23.3% average reduction in group size! To further test, I dug out my throater reamer and rethroated some of the CLE chambers (2.450" long) to Wylde specs (2.475"), then again to 2.50", and finally to a NATO length of 2.550". Retesting under the same conditions, the additional the 0.025" length from CLE to a Wylde spec of 2.475" increased these barrel’s group size about 23% larger, just as in the initial tests.

The additional 0.025 to 2.50" made the groups worse, and increasing again to the NATO length was even more horrible. The obvious conclusion is another example of encyclopedic error. Despite the initial claim of being jump proof, this isn’t the case. Barrels chambered with longer freebores will wear out sooner. Brass Sorting Competition shooters and handloaders love to sort things. They spend countless hours doing so trying to gain an advantage.

While these sorting chores don’t seem to hurt anybody, I am not sure that it really makes ammo any better. A common sorting activity involves weighing brass. The encyclopedic error in this endeavor is the conviction that heavy brass has thicker walls, thus having less internal volume which should pressure more and perhaps producing a little higher velocity.

Long Palma barrel (top) showed only a 7 fps improvement in velocity consistency due to brass weight sorting. Consistent velocity is a good thing. Inconsistent muzzle velocities will lead to vertically stringing and egg-shaped groups, especially at long distances. Faster bullets will hit higher and the slower bullets will impact lower.

A quick mental calculation fairly accurate with 80 and 90 grain .224 bullets is every 10 feet per second velocity change results in a vertical displacement of an inch at 600 yards and three inches at 1,000 yards. Given a rifle capable of one minute groups at 600 yards, a 30 fps velocity spread will yield a six-inch wide group nineinches tall. The MR-1 target shot at 600 yards has 12-inch 10 ring. This leaves much less room for error. Reducing this is valuable, hence the interest in sorting.

I am not the only skeptic regarding weight sorting brass. Others have conducted tests but most of them are similar: Weigh the empty case, fill it with water to the case mouth and weigh again. I don’t know if this was borrowed from race car engine builders who have been using a similar technique to "true" engine heads for decades. I don’t claim to have read all ballistic studies, but of those I have there does not seem to be a 1:1 correlation between case weight and water volume held.

At best, it’s a casual relationship. I didn’t repeat these water tests. The real point is determining a velocity relationship between varying casing weights to justify time spent sorting. At the time I was considering this, members of the USAR Shooting Team were sorting tens of thousands of cases each year to 1/10 grain increments so I had access to a large range of cases of varying weights.

For my test, I selected ten cases, one each from the five bins on the heavy side and one each from the five bins on the light side. Those ten casings were all different weights and as far apart in weights as possible. The second batch of ten cases were of identical weight in the middle of the bell curve. To ensure equal propellant weight, I measured with a lab-grade scale accurate to 0.01 grain, more accurate than typical powder scales accurate to "only" 0.1 grain.

Uniform bullets were seated and measured to equal depth and a reputable, state-of-theart Oehler chronograph measured velocities fired under equal lighting conditions. There was no difference in velocity spread between the two samples! I repeated the process using several other guns with no change. I was using 20" AR-15 Service Rifle uppers with Wylde chambers initially and have repeated this test with other setups over the years, all with no changes in the result.

I have wondered why there wasn’t a velocity difference. Initially, I thought 20" Service Rifle barrels with fat gas gun chambers might not develop enough consistency for case variations to matter. I was using brand new Lake City brass with primers crimped in place at the factory. Manufacturers of military brass don’t perform all the fancy flash hole work that more expensive custom brass makers such as Lapua claim to do. Also, some commercial primers have reputations for better velocity consistency than others.

I considered that perhaps primers had some vote in the matter. Regardless, I was a military shooting team armorer at the time and felt obligated to run the study with what we actually used. I did address the barrel length variable in subsequent testing with 26" Match Rifle uppers. In keeping the ammunition and chamber the same, I found the additional barrel length didn’t matter there. The normal 20" Service Rifle configuration is the most common AR configuration with 26" Match Rifles second.

Since leaving the Reserves, I have built 30 and 32" Palma configurations. Given no need for magazine feeding, I use tighter chambers similar to bolt actions. In building such a rifle for a customer with a 32" barrel and tight chamber, he knew of my previous velocity spread tests and offered to provide sorted Lapua brass for anew test. He used a sorting method similar to mine and loaded with a slower burning powder (Vihtavuori N150) instead of Reloder 15 or Vihtavuori N140 more common in 20 and 26" barrels.

This test was with a longer barrel, tighter chamber, Lapua brass instead of military L. C. cases, and different primers. I admit this is too many variable changes for a test but that’s the hand I was dealt. However, the ammo loaded in consistent, same-weight cases chronographed 7 fps better than those loaded in cases with purposely-different weights. I readily admit this slight improvement may be random and within normal margin of error.

I used multiple uppers in previous tests and would like to repeat this one in more than one rifle. It is possible the modest improvement in this recent test may be with variables other than brass weight, such as the tighter chamber. Lake City brass is commonly used by Service Rifle and Match Rifle shooters, the stick powders I tested (RL-15 and VV N140) are often used with 80 and 90 grain bullets, and Wylde chambers are popular in match AR-15s. My tests influenced me to discontinue weight sorting of L. C. brass for

use in 20" and 26" barrels with fat gas gun chambers, however, anyone that feels such variables justify a retest, please do so! Cooking Ammo One of the stages in the rifle National Match Course is 20 rounds for record from prone at 600 yards fired in 20 minutes. Obviously, chambers can heat significantly.

It has been posited for decades, going back to at least the M14 era, that allowing around to reside in a hot chamber for too long heats up the cartridge and it will shoot at a faster-than-normal velocity, resulting in a flier. While I don’t remember everything from my college chemistry courses, I do recall that most chemical reactions do take place more vigorously in higher temperatures. Many have noticed on hot days that ammunition achieves higher muzzle velocities and pressures.

To test "ammunition cooking", I went through a 50 round box of Black Hills 77 grain match ammo, picking out the two most concentric rounds and charged them first in a 30 round mag, making them shots 29 and 30 when firing. Because I was actually shooting a group, I didn’t want poor cartridge concentricity to throw those final two "cooked" rounds out of the group. I filled the magazine with 28 more rounds from the same box.

I was testing in Pennsylvania just after Christmas on an unseasonably "warm" day of 40 degrees so I had to warm up the barrel as it started colder than guns are during the summer heat at most big High Power competitions. Warming up with 28 rounds exceeds the number that would normally be fired. Following those shots, I left the last two rounds in the chamber for two minutes each, a longer delay than would normally be encountered in a match.

The group of 28 rounds ended up being a respectable 1 1/8" wide by 1 1/8" but a bit fatter than it should have been as the test gun consistently shot ten rounds groups around 9/16" during previous testing. The buffer spring in my lower had recently split and I had just thrown out the broken section, inserted the buffer in the long remaining section, and driven on.

Well, that decision came back to sort of bite me in the butt during this testing as I encountered over a half dozen failures to chamber in this test firing. I ended up messing around getting rounds chambered to fire, which may have caused them to be positioned less than uniformly in the chamber. Given that uniform positioning is important, this group could have been tighter. I fired the first 28 rounds as fast as I could, pushing the machine rest forward and back into battery while clearing the failures to feed.

Round #29 cooked with the bolt closed for two minutes and it went 1 3/8" away from the group toward 5 o’clock, more than doubling the size and with a velocity of 2,827 fps. I chambered round #30 and waited two more minutes. It also went out at 5 o’clock at 2,816 fps. If fired at 600 yards on an MR-1 these likely would have ended up in the nine ring. That is mild compared to cooked-round fliers I’ve observed through the spotting scope. The average velocity 2,753 includes the cooked rounds.

Discounting those two, the average was 2,746 fps. Subtracting the fastest cooked velocity of 2,827 a thirty round 2,753 average is a significant 74 fps difference. This gives credence to the cooked round theory. Beyond a test, cooked rounds absolutely demonstrate changes in practice and any experience shooter has seen this happen.

Spotting shooters at various matches over the years, I’d sometimes use a stop watch to time how long someone let a cartridge sit in the chamber before firing it and could accurately predict if they’d have a flier! I’ve experienced this as a competitor myself. Don’t let a cartridge sit in a hot chamber! I believe the velocity increase of cooked rounds is only part of the cause.

If velocity increase was the only factor, all cooked rounds would go high, however, my formal test verifies this isn’t always the case as my tested cooked rounds impacted low, being out at 5 o’clock. This is consistent with what I’ve observed in decades of range observations. Although I didn’t keep formal records of these various range observations, I’ve seen cooked rounds deviate in all four quadrants of the target with corner shots being common.

I don’t remember high fliers as more common than low at 4, 5, 7, and 8 o’clock. Although the two fliers in my machine rest test would have scored 9s, I frequently saw fliers out in the 8 and 7 rings, even from Master and High Master competitors that should have known better. Competition shooting causes stress on everyone and even champions can make mental mistakes occasionally. Beyond velocity changes, I wondered if casings were changing dimension due to the heating.

I took four dimensional readings of a .223 match round before putting it in a ballistic oven for two minutes. Remeasuring revealed those four readings increased by 0.0005" each, indicating heat causes ammo to swell.

This goes back to the importance of uniform positioning of the cartridge in the chamber and on the bolt face. One of the four measurements was the diameter at the neck which influences neck tension. Brass isn’t perfectly uniform regarding case wall thickness and may be relevant to cooked round fliers. I would expect that brass on the thin side of the neck to expand more than the thicker side when heated, releasing the bullet more when fired and tipping as it enters the rifling.

Since the shooter does not know which side of the neck is thinner, cases are positioned randomly and cookedround fliers could go in different directions. Changes in brass dimensions causing varying positioning of the case in the chamber and on the bolt face may conspire with changes in neck tension on the bullet. With all these factors conspiring with changes in velocity as well as factors that many of us haven’t thought, it may paint a full picture of fliers due to heated ammunition.

Nobody seems to talk about it, but I believe another factor of cookedround fliers is shooter error and fatigue. While that round is trapped and cooking in a hot chamber, the shooter is likewise trapped in a heavy "iron maiden" shooting coat and also "cooking." A leather sling is tightly constricting his support arm, cutting off circulation, and making his hand numb. Vision is suffering, causing issues with sight alignment.

During those periods of cooking, light and wind conditions may also change and missed unless the shooter is being very vigilant. Regardless of the actual mechanism, cooked-round fliers do occur. In case you’re wondering why I include an assessment that has proven true in an article on encyclopedic error, many folks claim velocity increase is the sole culprit but that isn’t true. The fix is to avoid chambering around until you’re ready to fire.

This is especially important later in longer strings when the chamber is heated up more. Should firing be delayed with a chambered round, unchamber it, put it last in your ammo queue for record fire, and substitute a cool round in its place. Each rifle will behave individually when it comes to cooked rounds. Ammo will also have a vote. I fired commercial ammo in my test loaded with ball powder which has a reputation as being more susceptible to temperature changes. However, most of them burn a little cooler.

Most folks handload stick powders for use in long range slow fire strings where ammo cooking is most common and these propellants are reported to be a little less susceptible to temperature changes but burn hotter, potentially heating up chambers a little more. Chromoly vs. Stainless Barrels Several decades ago, stainless steel barrels began making inroads in the hunting fraternity. This made some sense as hunters are sometimes out in inclement weather and wanted the corrosion protection for their rifles.

It wasn’t long before gun writers published articles extolling lavish claims for stainless. One of those claims was superior accuracy. Barrel manufacturers jumped on the bandwagon. Stainless is easier to machine using the button rifling method so barrel makers were quick to promote it. Plus, they found the market supported them charging extra for it. When I started as Reserve Team Armorer we didn’t have spare barrels or parts.

When I did receive a budget to purchase replacement barrels, I bought equal numbers of stainless steel and chrominum-molybdenum alloy and over the years worked with match AR barrels from every custom barrel maker in the country. As I installed them I tested using known ammunition lots and kept meticulous records regarding group sizes and fliers. After testing hundreds of match barrels I finally analyzed my accuracy results.

From every manufacturer offering both stainless and chromoly barrels, the chromoly shot better. They consistently had tighter groups with less fliers with 50 percent of those tested shooting better than average while only 41 percent of the stainless could make the same claim. 28 percent of stainless barrels shot fatter than average groups while only 15 percent of the chromoly barrels did so. When all the groups were compared, chromoly shot 9.6 percent tighter than stainless.

Despite these measured differences, I’m not trying to convince you against stainless barrels. I am hoping that you won’t dismiss chromoly. Customers have been conditioned by years of encyclopedic error that stainless is more accurate when tests show otherwise. All we gunsmiths can do is offer facts as a balance. At the end of the day, we’ll build whatever the customer wants and can afford.

Tight upper-to-lower fit in Stoner rifles is equally important to obtaining high accuracy performance. Upper/Lower Fit I dedicated an article on this topic and will only review the high points here. It’s accepted that slide-toframe fit is important in precision handguns and tight bedding aids in bolt action rifle accuracy. However, for some reason, some people are convinced the fit between the upper and lower receiver of an AR- 15 doesn’t matter.

I believe firearms have more in common than many realize and suspected that AR-15 upper-to-lower fit also mattered. Early on as USAR Team Armorer, I was machine rest testing all of their competition Service Rifle uppers. I used the same Colt lower with all and would characterized its fit to most of these uppers as average. Accuracy results were horrible, with most uppers shooting ten shot groups with match ammo in excess of one minute. With several dozen uppers tested, I had a nice sample size.

I cleaned the bolt carrier assemblies and bores of these uppers, then installed a tight Accu-Wedge in the lower before resting all of them. Even in a machine rest, the tighter upper-to-lower fit with the Accu- Wedge reduced group sizes an average of 26 percent! The Accu-Wedge is a cheap and easy method of dealing with slop in this fit and more can be done, but this fit does matter. Conclusions We’ve covered a number of encyclopedic errors common to the AR-15, a firearm that has been around for about a half century.

The over twice that old and the M1 Garand falls right about in the middle. I’m betting that firearms in circulation that long have encyclopedic errors attached to them as well. If you know of other encyclopedic errors associated with firearms you work on, why not take a little time to test and write them up? Submit your observations to this magazine so the rest of us can be better informed. AG American Gunsmith Reader Services 1.