How to Develop Accurate, High Performance Handloads
Date: Jun 12 2007
Case Inspection, Preparation and Priming
Before proceeding with load development for any cartridge, it is imperative to properly prepare cases. Previously fired cases should be inspected for defects, including splits in the mouth and body. Look for signs of case head separation (just forward of the head in the case body) in the form of a shiny area on the outside of the case, or it can be felt with a small L-shaped wire from inside the case. Cases with signs of corrosion may be weakened. If cases are older and have been stored with fired primers in place, corrosion inside the primer pocket can lead to primer pocket leakage (darkening around the outer edges of a fired primer). Brass with any of the above defects should be discarded, as it is somewhat risky to reload.
Bottleneck rifle cases are usually full-length sized, while those prepared for semiautomatic, pump action and certain lever-action guns are generally sized in a small base sizing die to assure proper chambering. Be certain that dies are adjusted correctly when performing this operation, or case life can be shortened and accuracy may suffer. (Most die manufacturers offer detailed instructions.) To obtain reliable chambering and proper bullet-to-case fit, straight-wall handgun cases should be full-length sized, and case length for rifle and handgun cartridges should be measured to be certain that they are within maximum limits and trimmed if necessary. Cases that are excessively long might not chamber or can cause dangerous pressures when fired. It is preferable to begin with cases from one maker and of the same lot number, which will give the most uniform results in determining pressure and accuracy.
Priming is an often overlooked step of handloading, but plays an important role in how ammunition performs. Generally primers should be seated .003 to .005 inch below flush. In this fashion the anvil legs should be in full contact with the bottom of the primer pocket and will give reliable ignition when struck by the firing pin.
Choosing the correct primer is also of paramount importance. Let’s say we are handloading the .44 Magnum. Naturally it takes a Large Pistol primer, but many deduct that since it’s a magnum cartridge it will require Large Pistol Magnum primers. Unfortunately it is not that simple. There are many excellent powders for loading the .44 Magnum that actually give better accuracy and less pressure when used in conjunction with standard primers. On the other hand, there are many other powders that need a Magnum primer to ignite correctly, and using a standard primer has proven (in laboratories) to produce erratic pressures and velocities. While the .44 Magnum has been used as an example, similar results can be seen with other cartridges, both pistol and rifle.
Generally the best way to determine the ideal primer for pistol cartridges is to seek guidance from the
powder manufacturer. The same advice applies to rifle cartridges, but logic would dictate that large capacity and most magnum rounds will perform better with a hotter Magnum primer, while smaller capacity and non-magnum rounds are generally best served with standard primers. After determining what powder (or powders) will be used, then the correct primer can be chosen.
Developing Loads for High-Pressure Bottleneck Rifle Cartridges
After cases are inspected, sized, trimmed (if necessary) and primed, let’s begin developing a load. Unless one has education and experience at developing load. Unless one has education and experience at developing loads, published data should always be referenced. Do not use loads from unknown sources, which seems prevalent on the Internet. Most reloading manuals list powder charges that have been carefully pressure tested. The “beginning” or “starting” loads are usually at least 5 percent below maximum. Having experience at developing handloads for more than 150 different cartridges and many more guns than that, I must emphasize the importance of beginning with “starting” loads before attempting “maximum” loads. Not all guns for a given cartridge share identical dimensions. A short throat, an abrupt leade, tight groove diameter or other small tolerance changes can cause pressures to spike in a given gun, while the same load was safe in the test gun or pressure barrel. Excess headspace, an out-of-spec firing pin or firing pin hole and other issues can cause a primer to rupture. Again, don’t start with maximum loads.
After charging cases with a “beginning” powder charge, seat bullets to correspond with suggested SAAMI overall cartridge length; they should more or less duplicate factory ammunition lengths. (More on bullet seating depth and overall cartridge length in a moment.)
Fire a few rounds, carefully checking each case for signs of excess pressure. (This is where a chronograph is valuable in determining if a load is close to duplicating factory loads or the advertised velocity of the load you have selected. If speed is similar (and with correct powders), pressure is probably similar too. Contrary to what has been widely published, primer appearance is not always a good indicator of pressures, as there are simply too many variables. Nonetheless there should be no signs of rupturing. Primers that are pierced and/or cratered (wherein the firing pin indentation is pushed back) can indicate excess pressure but is often due to a rough firing pin that is incorrectly shaped or too long. Cratered primers are often the result of a poor fitting firing pin/firing pin hole or a firing pin spring that is too weak. Flattened primers do not necessarily indicate the load has excess pressure or is
Many factory loads fired in production rifles will have flattened primers. On the other hand, if one load is flattening primers more than another (at least if primers are of the same type and manufacture), it is probably generating more pressure. Another issue that can flatten primers excessively is excess headspace. If any of the above issues appear with your factory ammunition or handloads that are within normal load specifications, you should have a qualified gunsmith examine your rifle before proceeding.
At this point a blade-type caliper that is capable of measuring 0.0001 inch will prove a valuable tool in determining the safety and approximate pressure of your handload. If you are using new, unfired cases to develop your new load, case head expansion may vary more than cases that have been once-fired prior to developing loads. It is better to begin with once-fired cases, as their webs will be settled and readings will be more accurate. Cases should be of the same make, as hardness varies by manufacturer and so will case head expansion. Measuring the diameter of the head, just above the extractor slot but below the case body in the web area, before and after firing will give an indication of pressure. Most modern high-velocity bottleneck cartridges, such as the .243 Winchester, .270 Winchester, .308 Winchester as well as the 7mm Remington Magnum and similar rounds, will expand case heads .0003 to .0005 inch and are generally considered to be around 50,000 CUP (not psi). This is approximately equal to
most factory loads and is generally considered maximum.
Assuming your starting loads are below maximum pressures, fire a few groups (from a proper sandbag rest) to see how that load is performing in your gun, then record their sizes. In an attempt to fine-tune the load, seating bullets out closer to the rifling will often, but not always, increase accuracy. The maximum overall cartridge length (or just how far we can seat bullets out) is usually determined by two factors in typical bolt-action repeating rifles. First, bullets must fit and function correctly in the magazine, and second they must chamber properly. Single-shot rifles are only affected by overall cartridge length, while tubular magazine guns (leverguns, pumps, etc.) must feed correctly and are sensitive to overall cartridge length.