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Ten Steps For Custom Varmint Cartridges

by Steve Comus


        Consistency is the essence of accuracy. The object is to put every bullet in the target as close to the one before it and the one after it as possible. For most rifles, this means custom loading the ammo to achieve maximum accuracy.

         With this in mind, what are some of the most important things that can be done to ensure consistency, round to round? The giant step is to do everything possible make every component consistent within itself. Then, as a result of good bench technique, it is important to make the combination of components within each cartridge as consistent as possible.

         This starts out with the brass case. It is suggested that all cases within a batch be from the same manufacturer and, if possible, from the same production run from that manufacturer. This is close enough for some, but not for the really serious shooter. Within the same production run from the same manufacturer, there can be variances in the individual cases. Before beginning, then, it is a good idea to check each case and discard those that are very far out of spec on the scale, whether the scale in question is one that weighs the case or a comparator. The amount of acceptable variance depends upon the shooter, but the closer each case is to the other, the better.

          Another matter that is assumed here is that all of the cases will be clean. Dirt is bad. It is not necessary for the cases to be polished and shiny: That is more indicative of pride of operation than actual accuracy. However, the cases must be clean or many of the other steps are irrelevant.

1. Primer Pocket Uniforming

          Now we’re ready for the first step -- uniforming the primer pockets of the cases. By uniforming, we mean that the pocket must be squared to the case and that the depth of each pocket needs to be the same.

          This way, each primer can be seated at the same depth and will be resting uniformly against the bottom of the pocket. Although there are hand tools to accomplish this procedure, using a fixture and a precise drill press is helpful for several reasons, among which are the ability to duplicate efforts and to do so expediently.

2. Flash Hole Uniforming

          It is generally accepted that the flash hole in the primer pocket needs to be in the middle of the primer pocket. Some are not. Those should be discarded before the preparation procedure begins, so for this writing it will be assumed that all flash holes are well centered in the many pieces of brass.

          Assuming that, it is time to run a small drill through the hole to ensure that the holes in the various pieces of brass are uniform in size, and to take off any burrs that might interfere with the transfer of the fire from the primer to the powder charge.

          Again, there are handy hand tools for this job, but it is worthwhile to set up a drill press system to keep everything uniform over time.

3. Sizing The Case

         The case needs to be sized properly, and the entire run of cases needs to be sized uniformly. This may sound simple, but there are ways to screw up and there are ways to do it right.

          For example, how you adjust the sizing die is important. The ideal scenario is to size the case only enough to make it fit as closely as possible to the chamber of the rifle from which the ammo will be shot.

          Although perfectly good ammo can be constructed with run-of-the-mill sizing dies, it really is worth the price to invest in a set of match or even custom dies. These dies tend to be kept to tighter tolerances than are the standard offerings of the various companies.

          Also included in this definition of sizing is case trimming. That’s right, it’s better to trim each case after it has been sized. That way, every single case is uniform in length when it is actually loaded.

4. Case Neck Uniforming

The wall of the case neck typically is not of uniform thickness around its entire circumference. This can contribute to inconsistency in bullet let-off at the time of the shot, so it is necessary to make the neck uniform.

          There are two general ways to accomplish this. One is outside turning of the neck and the other is inside reaming. If the neck is reamed inside while the case itself is in a proper die that constrains the outside of the neck, the reaming will be uniform case to case, and the neck will be squared with the rest of the case. This is important.

5. Compare The Brass

          Once the cases have been prepared, it is time to compare them, one to another. Simply weighing them is not enough: Several other things need to be determined. For example, it is important that each case is uniform to its own center axis and uniform throughout.

          To determine this, one must use what is called a comparator. For this, I made a trip to David Miller Rifles in Tucson, Arizona, where the use of a comparator is common. Miller makes some of the most accurate hunting rifles in the business. Vern Juenke makes the most common comparator currently available. This electronic measuring device (known alternately as an internal concentricity comparator or an ultrasonic metal mass detector) quantifies the degree to which a case is uniform to any other case.

          By preparing large lots of brass at one time, it is possible to create sub-groups of cases, all of which are comparatively close in all dimensions to the others in their sub-grouping.

          This step allows the shooter to discard any case that is significantly out of spec, compared to the others. The use of this device also eliminates the need to weigh the cases or bullets ahead of time. The comparator will reject inconsistencies of any kind.

6. Proper Primers

         The subject of primers is of some controversy among shooters. Primers from the various major manufacturers are superb overall and it is possible to load extremely accurate ammo with generic primers. But why go through all of the other steps and overlook the primer’s possible contribution to consistency?

          Match primers cost so very little more than generic primers that it doesn’t make much sense not to use them, especially when you are investing a lot of time in making custom loads.

          In all probability, the only difference between some match primers and run-of-the-mill primers is that certain lots that test more uniformly are packaged as match primers. But why not go for the ones that sample-tested more consistently?

7. Powder Charge

          Some powders work more uniformly in some cartridges than others do, and some powders work better in some rifles than others. The first step is to determine which kind of powder works best in a particular rig. This is determined by establishing which powder produces the desired velocity within safe parameters, then isolating the single powder that, through a given rig, delivers the lowest standard deviation. For custom loadings, standard deviations of less than 10 are considered exceptional. Deviations of more than 20 are really not that good.

          Again, there are differing opinions about how one should measure the powder charge, once the proper charge is determined. Some insist that each charge should be weighed individually. Others opine that the volume needs to be uniform, even though there can be and is some variance in weight to volume over time, even from the same can of powder.

          The short answer is that if one is merely comparing cartridges that are all loaded at one time in one batch, uniforming the weight is a good way to go. However, if the same charge is to be loaded over time from the same can of powder, or from various cans of the same kind of powder, then it is likely that a precise volume measuring device that is not adjusted once set up is the way to go.

8. Bullet Choice

          Use of proper bullets is bedrock in importance. For this particular point, the discussion will focus on aerodynamic design and terminal performance characteristics. For example, is a boat-tail meaningful for the intended use? Does the ogive need to be radiused or secant in design? What about the terminal performance characteristics -- does the bullet need to expand instantly and violently? Does it need to penetrate only a little? Does it need to zip all the way through, leaving a caliber-size hole?

          Once the configuration and weight of the bullet desired is determined, it is important to choose a type and make of bullet that will probably be available over a long period of time -- one that is also intended to deliver accuracy.

          Most of the premium bullets that are tagged as "varmint" or "match" tend to be more accurate in more rifles than the standard hunting bullet incarnations -- but not always. It takes a lot of trial and error on the part of the shooter to determine which is best. But remember there is a "best" for each rifle. It is up to the shooter to determine what that is.

9. Compare The Bullets

         Just as each case needs to be compared to others in a batch, so do the bullets. A comparator can help eliminate unwanted "fliers" in groups by exposing bullets that are out of alignment with their own center axis, bullets that are out of spec in the ogive, shank or tail, or even those that have voids or other flaws in the their lead cores or inconsistencies in the jackets.

          All of these things can be detected via use of the comparator. To be blunt, it is ludicrous not to use a comparator when loading precise ammo. These devices are not terribly expensive, and they can help in numerous ways.

10. Seating Depth

         Proper seating depth is a subject of much discussion among shooters. Some chambers and rigs are intended to use ammo that has the bullet touch or almost touch the lands of the barrel. Others are designed to use some degree of lead (free travel) of the bullet from the time the shot begins until the bullet engages the lands.

          Pressures can vary tremendously, depending upon the seating depth for some cartridges in some barrels. That is the subject of another discussion. Here, it will be assumed that the proper seating depth for desired and safe performance has been determined.

          Now the important thing is to ensure that each bullet is seated uniformly. This means that the seating die itself must be adjusted properly and uniformly. It also means that it is necessary to seat each bullet as squarely as possible to the axis of the case.

          Most match dies or custom dies feature some form of floating collar that guides the bullet squarely as it is being seated into the case. This kind of die should be considered basic for true custom loadings.

          Some of these steps may be quite obvious, while others may sound somewhat extreme. But precision loading involves the combination of all logical steps, as well as those esoteric ones which, both individually and in concert, result in consistency. After all, that is the essence of accuracy.

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