Brownells 75th Anniversary - A Shooting Heritage

Steps to Minimize Bullet Run-Out

On a daily basis in the Sinclair Call Center, our team of Reloading Technicians are assisting fellow reloaders with questions, suggestions, or issues they are having with their process. One of the most commonly asked or discussed topic is bullet run-out. Run-out can be described as how much the entire loaded round is out of a true straight line from center point on the case head to the point of the bullet.Run-Out is more formally known as concentricity of an object. “Concentric” comes from the Latin wordfor “common center”. True concentricity is an object sharing a common center point or axis throughout. When measuring bullet run out you are checking everything from your reloading sequence has properly worked to create a loaded round that is as close to concentric as possible. Poor bullet run-out can cause poor and inconsistent accuracy, and variations in bullet velocities. The truer the loaded round the more consistent your results will be on paper and across the chronograph.

As most of us know we do not live in a perfect world. Even with the most care taken in reloading including detailed case prep, extra care taken in the process with top end die and press set up, etc, run-out can and will still occur. There are some steps that can be taken in your reloading sequence at the bench and even with your tools that can minimize bullet run-out. Before we jump into these areas let’s go over how to properly measure run-out.

Run-out is generally measured in thousandths of an inch with a concentricity gauge. There are many options of concentricity gauges to choose from that work well. Some work on loaded rounds only, some have a bullet straightening feature, and a few work on both loaded rounds and empty cases for checking case neck concentricity. The tool of choice by the Sinclair Reloading Tech Staff is the Sinclair Concentricity Gauge (Part # 09-175).

This tool is a mainstay on my bench, and it is used about as much as I use my reloading press! The tool uses two sets of bearings that are set on lateral length adjustable anodized aluminum blocks to accommodate cartridges from .221 Fireball sized cases up to .50 BMG. The indicator is set on a height adjustable swiveling base on a stand that can be used for checking bullet or case neck run-out. The adjustable blocks ride aligned in a precision milled slot. The entire set up is on an anodized base plate that gives excellent support during the process that is crucial to operation and accuracy. Basically the operation consists of placing a loaded round (for checking bullet run-out) or an empty case (for case run-out) on the bearings with the indicator end touching the chosen point to be measured. The case is easily spun with one finger as the indicator measures the amount of run-out. Once this process has been done a few times it is a fast and accurate means of measurement. In terms of indicator type being used, whether dial or digital, I actually prefer a standard dial indicator (pictured below) over the digital type. My reason for this choice is that you can see the needle jump when run-out is present. I believe this to be easier and faster than looking at digital numbers while measuring.

Sinclair Concentricity Gauge w/dial indicator
Sinclair Concentricity Gauge w/dial indicator

Case Prep Steps to Minimize Run-Out

As mentioned earlier, there are a few steps that can be taken in your reloading process that can help minimize bullet run-out. The first steps that can be taken are in your case prep regiment. One of the first areas to look into with new brass is to check neck wall thickness consistency. You are looking for cases that have case necks that have fairly consistent thickness around the diameter. Using a tool such as the Sinclair Case Neck Sorting Tool (Part # 59-1000) can quickly help you determine the consistency of the thickness of the neck walls. Standard brass may have a thickness variance as much as one to two thousandths of an inch. Higher quality brass will have a more consistent neck wall thickness with little or no variance. Inconsistent neck wall thickness can cause bullet run-out since different pressures are applied to the diameter of the seated bullet. Either sort through and cull your brass for consistent walls or perform a “cleaning cut” by neck turning the difference in consistency off the necks of the entire lot to create common consistency. (Neck turning is a whole other cup of tea and will be discussed in future features).

Other areas of case prep that can make a difference in bullet run-out is to maintain consistent case length and trim when needed, lightly inside chamfer and outside de-burr the case mouths. I prefer the Sinclair 28 degree “VLD” inside case mouth chamfering tool (Part # 26-6250) for most of my rifle and even pistol case prep. Additionally clean out and wipe off the necks of the cases once prep time is finished.

Sizing Steps to Minimize Run-Out

One of the most common steps in the reloading process that contributes to bullet run-out occurs is the sizing operation. If improper techniques are used or there are issues with the sizing die set up, a once perfectly concentric case can become out of whack. By using the proper dies for your application, properly setting up the die/shell holder or floating the de-capping/expander assembly, you can eliminate problems before they happen.

The choice sizing die by many of us on the technical staff is the Redding Type-S series of dies. These are full-Length or neck sizing dies that utilize a removable/changeable neck bushing (sold separately) to size the neck according to your application. These dies are machined with true precision and quality in mind. The Type-S dies come with a standard de-capping assembly with a caliber specific expander ball in place. In addition to this an undersized retainer to hold the de-capping pin is included with the die. In my experience with these dies I use the standard expander ball with new, unfired brass on the initial re-size. I will then use the undersized retainer in place of the expander ball with brass that has been fired. I have found this step crucial in my reloading regiment to minimize bullet run out. The use of the expander ball can cause a few thousandths of run-out when the case is being pulled back out of the sizing die. With the undersized retainer in place the only thing that touches the neck of the case in sizing is the bushing. If you prefer to use an expander ball, Redding offers caliber specific carbide floating expander balls that fit on the de-capping rod. This free floating expander ball will self center on the case neck, and reduce the amount of run-out that can be caused by a standard expander ball.

When setting up a Type-S sizing die, set the neck bushing into the die with the numbers facing down toward the body of the die. Tighten the de-capping assembly until it contacts the bushing and then back it off ¼ of a turn. This allows the bushing to free float in the die. You should be able to hear the bushing rattle if you shake the die. Having the bushing free floating self centers the neck, and again minimizes any run-out that can occur.

If you prefer other brands of sizing dies there are a few tricks that people use to minimize run-out as well. Many reloaders claim that the use of an “O”-ring at the base of the de-capping assembly lock nut will float the assembly and help self center during sizing. Another trick that has been used is to remove the retaining pin on the shell holder slot on the press ram, and use an “O”- ring in its place to hold the shell holder in place. This allows the shell holder to self center during sizing as well.

Seating Steps to Minimize Run-Out

Another common step in the reloading process where bullet run-out can be caused is in the bullet seating process. The first thing you can do is to use a high quality die with a sliding sleeve. The sliding sleeve perfectly aligns the case with the bullet to be seated. Good examples of these dies are the Redding Competition Micrometer bullet seating dies, Forster Ultra Seaters, or RCBS Competition Seating dies. All of these dies utilize a micrometer top to precisely set seating depth. They are all very high quality dies that have tight tolerances to maximize bullet straightness during seating.

Of the many questions we receive most of the callers are trying to seat long pointed bullets such as the Berger VLD or Hornady A-Max. One problem that the reloader faces with longer bullets is that they are so long that the standard seating die stem (the part that pushes the bullet into the case) is not machined deep enough to contact these bullets properly. The point of the bullet is “bottoming out” in the stem and the result is off center seating and/or rings and dents on the bullet nose. What should be done if you plan on using such bullets, is to purchase a “VLD” style seating stem, which is cut to accommodate the longer bullets. The use of this stem results in truer seating of the bullet without leaving a ring or marring the tip of the bullet.

Besides using a traditional press and threaded seating die another great way to get a true bullet seat is by using an arbor press and Wilson chamber type seating die. These dies are cut to very tight tolerances and have proven themselves for years as the main choice for bench rest enthusiasts. The design of the die positively aligns the case with the bullet as they are both captured by the die before the bullet is pushed straight into the case by the stem. These seating dies are available with the standard seating cap and stem or an additional micrometer top can be added for precise adjustment. Wilson also offers a stainless seating die with an integral micrometer seating head. This process is quick, true, and a great way to get the most out of your reloading!

Finally another trick used by many in the seating process is to turn the case while the bullet is being seated. Some people claim this will keep things straight. What they do is raise the ram in increments while seating and rotate the case in the shellholder in increments of 90 degrees from the original starting while the bullet is being seated. Personally I have tried this and have seen no significant difference at all. However you may be the judge of this one. It makes sense, and maybe I should try this a little more before I rule it out.

Bullet Straightening Tools

For those who want to mechanically straighten a loaded round there are a few tools out there that will help you true them up. The Hornady Lock- and- Load Concentricity Gauge (Part #050076) has a straightening feature. The gauge uses a threaded screw that you can tighten down on the bullet and observe how much you have straightened it out on the included dial indicator or how much more adjustment is needed. It can take a little bit of trial and error to get this just right, but it does work. Additionally there are other tools on the market that straighten out bullets. However, one concern that comes up is what are you doing to the neck of the case in terms of neck tension? If any of you have used these types of tool with success please post something on our blog and let your fellow reloaders know. From my experience it is time consuming, and I would rather spend my spare time loading and shooting.

Hornady Lock-N-Load Concentricity Gauge
Hornady Lock-N-Load Concentricity Gauge

Again, it is not a perfect world…

Whether you follow the aforementioned steps or processes or have tricks of your own and no matter how meticulous you are or how good your components or tools are; run-out will still show up. A reloader can drive themselves crazy trying to make each and every loaded round a true “0” in run-out. You will still see some minimal amount no matter what you do. Set yourself a standard of maximum allowable run-out for your loads. For instance for my Long Range 600 and 1000 yard F-Class loads I like to see .002” or less. I average .0015” and see a few in the range up to .004”. I spin each loaded round on my Sinclair Concentricity Gauge and sort them by run-out. Those that run over .002” I use for sighters or practice. I have tried to batch similar measured rounds together for competition, but have not seen a difference. However, I feel this gives me a sense of security knowing that I am shooting the truest loads possible. Run-out can make a difference in long range group consistency and minimizing the gap will maximize your potential. Not only will your loads shoot better but you will have one less thing to worry about when you are lining up the sights on the target. Now all you have to worry about is what forces of nature are on hand between you and the target.

Good Shooting!!!

Pete Petros
Lead Reloading Technician
NRA Certified Metallic Reloading Instructor

Sinclair International