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When Accuracy Counts: Case Selection and Initial Preparation
Part 1 of 4: Case Selection and Initial Preparation
Benchrest rifles are a collection of very fine tolerances. Your ammunition has to be held to the same high standard to make match-winning cartridges.
These articles aren’t meant to be a definitive guide to benchrest-grade handloading. That guide has already been written under the title “Precision Shooting Reloading Guide.” We have borrowed liberally and shamelessly from its opening article “An overview of Reloading for Extreme Accuracy” by Fred Sinclair and Bill Gravatt to create this quick guide. If you are interested in making truly accurate cartridges, this book is an excellent investment.
Rifles are a collection of tolerances. Benchrest rifles are a collection of even finer tolerances. Knowing this, it is easy to understand how minute differences in ammunition can effect accuracy. To make match-grade ammunition, the handloader has to hold their cartridges to the same high tolerances as the rifles in which they will be used. Little differences make bigger groups when it comes to loading for accuracy.
One Step at a Time
There are a number of steps to make extremely accurate ammunition, with each one leading logically to the next. Skipping one, or lowering the quality of the work done, will defeat the purpose of all the steps that follow. Thankfully, many of the most onerous tasks are one-time processes done before the first shot is fired. Once the brass has been selected and fully prepped, very little remains in the handloading process except re-priming and neck sizing throughout the remainder of the case’s life.
The forums are full of discussions on the merits of various brass manufactures. Some of the benchrest crowd would rather stay home than face a competition without the name Norma or Lapua stamped on the base of their cartridge. Frankly, in the PPC world, they are about the only game in town and their brass is quite good. But there are other manufacturers to consider, especially in larger capacity cases that fulfill both sporting and military applications. All of the American brass manufacturers turn out brass that is capable of match accuracy, so don’t write them off prematurely. When you do buy, get more brass than you think is needed and make sure they are from the same lot. This will help reduce internal variables that you otherwise could not control.
It is best to have a goal in mind for the total number of prepped cases you want to have on hand. Once you have that goal number, let’s say 50 cases that will go with you to the range for fire-forming, it is important to remember that about thirty percent of the cases you test will be rejected. So, get enough to allow for rejections. Reject early and come back to your “maybe” pile later if you are short. Making a good decision at this point will save frustration at the bench. The left over cases can be used later to set the neck turning tool and as range brass for initial zeroing.
Cases are mass produced items and malformed ones are relatively common. Inspect each case carefully looking for obvious defects. A bench mounted magnifying glass with light is a real help for the over-40 crowd like me. The main defects will be cracks in the neck or case body, crushed shoulders or deep creases in the neck. Next check the primer pocket. It is also fairly common to find flash holes that are damaged or, more rarely, not concentric to the primer pocket.
Imperfections like small dings in the case body, or necks that are not completely symmetrical do not have to be eliminated at this step. Damage of this sort is usually from loose packaging and usually has not seriously damaged the brass. Neck turning and fire-forming will iron out these largely cosmetic issues.
Handloading for accuracy means an investment in some new tools. A good quality electronic scale is a real help to precisely weigh large numbers of cases. Weighing cases gives the handloader insights into case dimensions that are not easily measured. Inconsistencies in web or wall thickness show up as weight variations. Selecting cases that are clos in weight is the easiest way to eliminate pressure changes caused by small internal differences that would otherwise would go unnoticed.
Creating a system for selecting cases by weight isn’t difficult. Of the ten cases I weighed from my lot, eight were within one grain of one another. Inside that group of eight, there were three that were within .4 grains. That is the group to use as a sample. Now add the three weights together and divide by three to get an average weight. In my sample it came out to 158.14 grains. I’m going to use a 2% variation as my threshold for rejection. In other words, a case can weigh 1% more or less than the average weight and still be accepted.
Because I am old and feeble-minded as well as blind, I like to write the acceptance numbers on a piece of paper by the scale. The high end acceptance number is done by multiplying the average weight by 101%. Our 158.14 average is multiplied by 1.01 to give a maximum weight of 159.72 grains. The low end is set by multiplying the average by .99 which makes it 156.56. Now weigh all of your cases and reject any which fall outside your guidelines. If you end up having quite a lot of brass pass this test, you may elect to reweigh with a tighter acceptance range of 1.5% or lower. The closer they are in weight, the higher the chance they will exhibit similar pressure characteristics.
Think of flash holes as something like a garden hose. The larger the diameter, the lower the pressure. Since consistency is the name of the game for accuracy, we are going to true the flash holes to one consistent size in a later step. For now, we are checking for oversized holes that are larger than our truing tool cutter. Most flash holes are around .082”, with the notable exception of the PPC which is usually closer to .062”. A #45 drill bit makes a handy gauge. It should fit into the flash hole easily but without much play. Reject any cases with oversize holes.
Primer Pocket Uniforming
Like flash holes, primer pockets are mass produced and prone to small dimensional changes. A uniforming tool is used to make the depth of each primer pocket consistent. In turn this allows similar firing pin strike depths on the primer which creates more consistent ignition characteristics.
A good uniforming tool should have a shoulder, or another positive stop, that sets the cutter’s depth. Its use is pretty straightforward. The cutter is inserted into the pocket and turned clockwise several times until the stop in flush with the case head and no more brass is removed from the juncture of the pocket’s base and sidewall. This a job best done by hand. You will feel when the cutting is finished by a change in how smoothly the cutter turns in the pocket. Very little material is actually removed; usually just enough to square the radius at the bottom of the pocket.
Flash Hole De-burring
Most flash holes are formed by punching, as opposed to more costly drilling, which tends to leave a jagged edge of brass inside the case body. A de-burring tool is used to chamfer the hole from the inside and give each piece of brass a consistent flash-hole diameter. This uniforms the primer’s spark intensity and flow into the powder column, reducing spikes in ignition pressure from case to case.
These tools are sold with caliber-specific pilots to keep the cutter parallel with the base of the cartridge. The Redding pilots used in this this story are intended for use with new, unfired cases and are sized to match the case mouth dimension. To use the tool, loosen the set screw and settle the pilot into the case mouth. Slowly push the cutter inside the case until it contacts the flash hole. Twist the tool clockwise several turns. You should see the cutter emerge into the primer pocket. Using a small penlight, you should be able to see a slight chamfer cut at the top of the flash hole. Once you have set the correct depth, tighten the set screw and move on to the next case.
Sore hands and the monotony of sorting, weighing, truing and chamfering brass can quickly become daunting. It is important to remember what you are doing with each piece of brass in the bigger picture. When finished, they will become the bedrock for all of the accuracy-inducing handloading tricks you will be performing. If a bad case is let in or you skip a step, your groups will suffer. The cases have to be as similar as you can make them. When you get tired or bored, it’s time to take a break. Benchrest handloading takes concentration. Know your limits and stop before you begin to make mistakes or cut corners.
Neck Turning: The Whys and the Hows