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More on Case-to-Bullet Concentricity and its Effect on 22 Rimfire Accuracy
By Frank Tirrell
[Originally published in the Summer 2005 issue of Small Caliber News]
[Scan of original article at the end]
A few issues back I wrote an article on this subject for Small Caliber News, which I thought had the subject pretty well covered. I had seen nothing about case-to-bullet concentricity in print for many years and just assumed that no one else was even thinking about the problem, never mind working on solving it. But then our illustrious leader, the “Big Kahuna” himself and mighty slayer of furry critters, Todd Kindler, sent me an e-mail marked “URGENT” about some boys in the great state of South Dakota who have been working on this very problem for years. It was politely suggested it might be in my best interest to contact these professionals, increase my intelligence level and get brought up to speed, so to speak. (He is so subtle.)
I am always interested in anyone pursuing the Holy Grail and immediately dialed up Nielson Brothers Arms, Inc. in Rapid City, SD. A 50-minute phone call later with Lester Nielson, one of the two brothers who run the company, had me totally convinced that these ole’ boys know their subject well and have really done their homework. I am well acquainted with the advantages of concentricity gauges. I was using one as far back as 1965, and I made one of the first in the country back when I was shooting centerfire benchrest. I could tell that the Nielson Brothers’ statements were not the result of random unsupported testing but rather based on years of documented tests within a series of controlled environments.
Their website states that gauging and separating loaded ammunition by amount of runout dramatically increases accuracy. I was most interested in how they made the gauge because I know from personal experience how difficult it is. I also wanted to know how accurate their gauge was, so I offered to do an evaluation test and article. My only condition – let the chips fall where they may. I simply refuse to color any tests I perform. They agreed.
At this point, I want to clarify that I do not usually get into evaluating products. I always leave that to the real professionals like my friend Dane Hobbs. I have never been able to understand how he finds the time to do the detailed research evident in every one of his superb product evaluations we see in SCN. So, don’t get all excited thinking I am going to get up to his level. It just ain’t going to happen! A few days after our phone call, the brown truck they won’t race rolls up to the ranch with a package from the Nielson boys in South Dakota. When I opened the package, I was absolutely amazed at what I saw. (At my age, I can assure you it takes a lot to amaze me.)
I have worked as a design engineer and tool and gauge maker, coupled with a lot of QA, for some thirty-odd years. So I consider myself a connoisseur of fine workmanship and sound design. I am here to tell you that these ole’ boys hit this one right on the money. Gauge people know that the true test of any gauge is its ability to repeat on any given dimension, and this gauge does exactly that. Not only is it a piece of art from a manufacturing and design standpoint, but the thing really works! I’m a little ashamed to admit to fondling this item for days prior to testing.
Informed shooters have known for years that a couple of alignment problems exist in rimfire that affect accuracy. First are dimensional problems associated with both rimfire chambers and ammunition. These can be eliminated if properly addressed – it just costs money. The second set of problems, which have been around since the beginning of the 22 rimfire cartridge, are associated with projectiles misaligned in loaded ammunition. Resolving these issues has proven to be much more elusive.
Let’s take a few minutes to acquaint you with a few specifics so you may better understand how each relates to the problem areas. First, we are going to look at both chamber and ammunition specifications. According to SAAMI specifications (the standard manufacturing dimensions used by all firearms manufacturers), the sporting chamber is .818 of and inch long with forward diameter of .227. This chamber is used in all production rifles expressly manufactured for sport shooting. Specifications for the match chamber or match rifle are quite different. The chamber is shortened to .643 of an inch, and its front diameter is reduced to .2248 of an inch.
SAAMI cartridge specifications further state that cases used in both production sport ammunition and match ammunition are identical in size with a length of .643 of an inch and a diameter of .221 of an inch. Comparing chamber specs to ammunitions specs, it is clear that the loaded round in the sporting chamber is never even close to being in alignment with the bore. This chamber is not only too long but too large, both of which are detrimental to superior accuracy. However, the same round placed in the much shorter match chamber is automatically centered or aligned to the bore by the relocated throat. This is good if improved accuracy is your goal.
Before I get too carried away here, let’s first agree on the fact that the ideal situation for superior accuracy is when the projectile is aligned exactly in the center of the bore. This is an accepted practice by enlightened gunsmiths who make super-accurate guns and who coincidentally at the end of the day of competition are most often called winners. Smiths that do not subscribe to this practice make guns that do not shoot quite as well and at the end of the day are merely participants in the competition.
So now you have a better understanding of the advantages of the match chamber over the standard sporting chamber and how it corrects the first of our accuracy-related problems. But we are not out of the woods quite yet. Remember the situation where a projectile is not in perfect alignment with the case? This is the elusive problem that shooters have been unable to control. One might say, “So what? If the match chamber is going to align it in the bore anyway, why should I be concerned? Besides, there is no way to straighten it out anyway.”
Pay close attention here because this is important. It has been proven repeatedly that a misaligned projectile in the best of chambers will not shoot well. F.W. Mann, Harold Vaughn and hundreds of others have performed repeated tests confirming that a bullet that starts crooked in the bore does not straighten out on its trip down the rifling. It exits one side first from the bore, then escaping gasses tip it even further off its intended centerline path. The projectile is propelled into a large gyroscopic spin. The unwanted result is larger groups.
Now for you hardcore non-believers, here are a few facts to get your attention. Fifty cartridges from eight brands (400 round) of ammunition were gauged for runout and produced the following data:
The error ratio of .001 at 50 yards is .100 or 10 to one. This means the cartridges with as little as .001 runout will take most of you right out of the X ring. Are you beginning to get a better understanding of where some of your flyers come from and how important the gauging of cartridges is to improve your accuracy?
For the first time in the history of rimfire, an instrument is available to determine the exact amount of projectile runout in a loaded round of ammunition. Sorting ammunition into runout groups of like dimensions, a shooter can select the best aligned ammunition for serious work while using the less aligned for practice. By gauging and sorting ammunition based on runout, shooters finally have a way to correct the elusive accuracy problem.
The Nielson Brothers’ gauge is the most efficient tool I have ever seen for determining 22-caliber rimfire projectile runout. Not only is it fast and easy to use but its repeatability is remarkable. Keep in mind this is a precision instrument and requires reasonable care. It should not be bounced around in the back of a pickup bed while mending fence or chasing coyotes in the back forty at warp drive.
For my accuracy tests, Nielson Brothers Arms included a gauge and several boxes of pre-gauged and numbered ammunition that I promptly re-measured. (I have this thing about trusting people when conducting serious test. No offense, boys.) In no case did my use of the gauge produce any variation from their previously indicated findings in the several hundred rounds of ammunition I checked. Accuracy tests were performed in my tunnel with a borrowed, much tweaked, restocked Model 52 Winchester, better know as the “Bean Shooter,” belonging to friend Dennis Chavez. I used Eley EPS lot number UFX 1315 ammunition.
I used the Nielson Concentricity Gauge to separate ammunition by projectile-to-case runout in variations of .001 of an inch. Testing produced the following aggs. For groups at fifty yards:
It is quite evident from such results that accuracy is dramatically improved when ammunition is gauged for runout. If you which to improve your present X count or group size and gain a distinct advantage on line, investing in one of these little jewels will be well worth your time and money. Needless to say, I have grown increasingly fond of this gauge, but I just noticed Lester included a return address UPS label so I could send it back to him. I wonder if that means I don’t get to keep it?
For a more detailed report on bullet concentricity and an in-depth look at results from several tests, including the U.S. Olympic Team, using the Nielson Brothers gauge feel free to contact the company.
Nielson Brothers Arms, Inc.
3006 Glenwood Drive
Rapid City, SD 57702
Keep ‘em in the hole.