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As an avid reloader, I try really, really hard to make sure that I seat my rifle bullets straight in the case so that they are perfectly centered and aligned with the case itself. As an avid shooter, I assume that ammo companies do the same for the rifle cartridges I buy. Why? If a bullet starts its journey from a crooked beginning, it’s probably not going to exhibit stellar accuracy and shot to shot consistency. I like to visualize a late-night Disco bowling gutter ball. You know, where that 16-pounder bounces from side to side all the way down the lane. Sure, you might get lucky and get a strike after the ball rattles down the lane, but your odds ain’t so hot of bowling a perfect 300.
Sure, even when using one rifle, there are some ammunition-related factors that contribute to accuracy and consistency, including, but certainly not limited to:
- Powder charge weight consistency
- Primer consistency
- Cartridge case length
- Overall length
- Distance between the bullet’s bearing surface and the rifling
- Bullet construction and uniformity
- Bullet jacket consistency
- Cartridge case mouth thickness and uniformity
- And so on…
I’m also thinking that the current distance between Jupiter’s four Galilean Moons and Toad Suck, Arkansas, has something to do with overall accuracy, but that’s admittedly more of a theory than a hard fact. The bottom line is that no single factor determines the accuracy or lack thereof.
However, one big contributor to poor group consistency is bullet concentricity in the case. Think of it this way, if you stuff a bullet into a cartridge case exactly straight, then a line from the center of the tip through the exact center of the base would continue on through the mathematical center of the case and out the center of the primer. Assuming the chamber of your rifle is cut decently well, and the barrel is in line with the chamber, then perfect bullet alignment with the case will result in the bullet being forced into the rifling oriented directly with its flight path. If you cram a bullet into the cartridge case crooked, then it will be angled off to one side of the chamber and barrel so it will engage the rifling off center. The barrel will get it more or less straightened out as the bullet travels through the rifling, but this tipsy beginning is bound to result in inconsistent points of impact.
Sometimes I just feel the need to get a little geeky and engage in some simple science. Fortunately, our friends at Midsouth Shooters Supply feel compelled to help support important knowledge work like this; because, science! They kindly loaned some ammo and gear to do a little investigative research.
To get a handle on the bullet concentricity issue, I borrowed a Hornady Bullet Concentricity Gauge from the Midsouth folks. This nifty little tool is handy whether you reload your own or stick to factory ammo. Its purpose is to figure out of the bullet is aligned perfectly with the centerline of the overall cartridge. It has a large piston at one end with a hollowed out, concave cut. This is where you rest the base of the cartridge, and the concave shape automatically centers the base. On the opposite side is another piston, this one spring-loaded, that holds the tip of the bullet. It also centers the projectile relative to the gauge. A spring-loaded sensor slides up and down a track between the two pistons, allowing you to place the probe of the gauge right on the bullet itself. Then you just rotate the cartridge case with your hand. If the feeler probe moves back and forth, then the bullet is not centered. The dial gauge shows you how many thousandths of an inch the projectile is off center. There’s also a thumbscrew with a polymer tip that you can use to correct out-of-alignment bullets, but we’ll get to that in a minute.
To get a baseline on what we ought to expect from known good ammunition, the Midsouth Shooters Supply folks sent along some Norma .223 Match Ammo ammunition. This ammo is topped with 77-grain Sierra Matchking bullets, which are about as close to top-of-the-line accuracy projectiles as you can get.
To check out the variance one might expect in various types of factory ammo, I randomly selected ten rounds from the supply of Norma Match 223. To keep things interesting, I didn’t pick more than three from any single box, so the 10 cartridges came out of four random boxes. This is match-quality ammo designed for accuracy, so I expected I would see some low concentricity variance numbers. To get a feel for how budget practice ammo might differ, I did the same for ten randomly selected rounds too. I won’t name the brand as I’m performing a bit of an unfair evaluation. As budget practice ammo, I don’t expect the same attention to detail with little things like concentricity, so I don’t want to penalize the company – they don’t advertise or price this as match grade ammo.
|Cartridge||Norma Match 223 77-grain Sierra Matchking (inches)||Practice ammo, 55-grain FMJ (inches)|
While I didn’t measure the full random routine from multiple boxes, I did some spot checks against other reasonably premium ammo to see just how concentric the Norma Match 223 was in comparison. I took a few measurements of a couple of different cartridges and averaged the results.
- Hornady 55-grain V-Max: .0025 inch
- Winchester PDX1 223 Defender 60-grain: .002 inch
- Federal Fusion MSR 62-grain: .003 inch
So do these differences matter? Comparing groups of different ammo against each other won’t tell us much about the single concentricity variable, so I decided to get a little scientific about the matter.
Breaking Good Ammunition
Here’s my public apology to the good folks at Norma Ammunition. I’m sorry I broke your ammo! How? Remember earlier when I said that the Hornady Concentricity Gauge has an adjustment screw to straighten out wayward ammo? Well, you can use that screw to foul up concentricity too. I pulled another random ten rounds of the 77-grain Norma Match-223, and, well, bent the crap out of them. It turns out it’s kinda hard to do too much damage, but I was able to get the bullets out of whack with the centerline by about five one-thousandths of an inch, or nearly five times the normal variance from the factory. My idea was to “break” these ten rounds, then fire a careful 100-yard group to see if there was any noticeable difference in precision.
To make things really interesting, I pulled another random ten rounds of the Norma Match-223 and ran them through the gauge to straighten them even more. With a little careful tuning, I was able to get all ten under one one-thousandth of an inch.
Are Concentric Bullets Significantly More Accurate?
I fired two ten-round groups from 100-yards using the same Armalite M-15 rifle I had used in all previous tests. The result? The “bent” ammo grouped ten shots into 3.01 inches. The concentric ammo put ten shots into 1.17 inches. That’s almost a three-fold difference.
While we’re admittedly not doing statistical analysis here, the results convinced me. I literally shot these groups from the same lot of ammo, within minutes of each other with the same rifle, and saw a dramatic performance difference. If you’ve got an accuracy itch that needs scratching, check out the Hornady Concentricity Gauge. It’ll help you tune not only hand loads, but factory ammo as well.
Midsouth Shooters is a great resource for products like the above pieces at great prices. The company is offering you the chance to win one of the items covered in this and future GunsAmerica articles on Midsouth’s products. Just click the link, and gain tons of entries right up until the giveaway scheduled for 11-23-16. In addition, you can receive a free copy of the 240-page Reloading and Shooting Supply catalog from Midsouth Shooters! For more than 45 years, Midsouth Shooters has provided reloaders and shooters top-quality supplies and great prices. Click on the link and sign up to receive your free copy. See why so many shooters across the country shop at Midsouth Shooters.
To enter the Midsouth Shooters’ GunsAmerica Giveaway contest, click this link:
To purchase the products reviewed in this piece, click these links: