When developing a new load, it is common for handloaders to consult multiple sources of published data. Bullet manufacturers are often checked first, followed by powder manufacturers when bullet-specific data is unavailable. In many cases, these sources do not agree.
Two reputable manuals may list different maximum charges, different velocities, or both for what appears to be the same cartridge, bullet weight, and powder. For the handloader, this creates an uncomfortable problem. If the components are the same, why isn’t the data?
This discrepancy raises two inevitable questions. First, which source should be trusted? Second, and more importantly, why don’t they agree in the first place?
This article is not about where to find load data, nor is it about substituting published data with forum anecdotes or software predictions. It is about understanding why conflicting data exists at all, even when it comes from reputable manufacturers using sound practices.
We will address the second question first. Once the sources of variation are understood, the first question largely answers itself.
Embracing Load Data Variation
Component Variation and Tolerance Stacking
Handloading is not an exact science. In an ideal world, 23.5 grains of H335 loaded in Federal .223 Remington brass, ignited by a CCI small rifle primer and pushing a 62-grain bullet, would always produce 2,950 feet per second from a 24-inch barrel. In practice, that level of consistency does not exist.
Experienced handloaders understand that variation is present in every component. Case capacity varies not only between brands of brass, but also within the same brand, produced on the same equipment. It is normal to see a 2–5 percent difference in case capacity between different lots of brass.
Powder is no different. Burn rate varies from lot to lot, even within the same product. A batch of H335 produced today may burn slightly faster or slower than a batch produced weeks earlier. While these differences are generally small, they are real and measurable.
Bullets also vary. Projectiles rarely weigh exactly their nominal value. Individual bullets commonly differ by a few tenths of a grain, and entire lots may trend slightly heavier or lighter than average.
Handloaders often consider these variations in isolation, but the real effect appears when they stack together. Consider a load assembled with brass that has four percent less internal capacity than average, paired with a powder lot that burns five percent faster, a bullet that is three-tenths of a grain heavier, and a primer lot that is slightly hotter than nominal. When all of these tolerances align in the same direction, the result can be significantly higher pressure and velocity than expected.
This type of tolerance stack, where every variable contributes in the same direction, is relatively uncommon, but it is considered normal within manufacturing limits.
Tolerances can also stack in the opposite direction. Brass with greater internal volume, slower-burning powder, cooler primers, and lighter bullets can all combine to produce lower-than-average pressure and velocity.
More often, tolerances partially offset one another. A case may have slightly more volume, the powder may burn a bit faster, the bullet may be close to nominal weight, and the primer may be hotter than average. In this scenario, the individual variations cancel out, producing pressure and velocity that appear perfectly average. From a performance standpoint, this is the ideal outcome.
When a manufacturer develops load data, all of this component variation is present. Technicians do not evaluate each component to determine where it falls within its tolerance range. They do what handloaders do: assemble the components and fire the test rounds.
The published data is therefore a snapshot of how a specific combination of components, from specific production lots, performed at that moment in time. If the same test were repeated months later in the same laboratory, using the same basic components but different lots, the results would likely differ—sometimes by more than handloaders expect.
Variation in the Testing
With any source of published load data, it is the responsibility of the publisher to disclose how that data was generated. Not every publisher provides this information, but when it is available, it offers critical insight into how the data should be interpreted.
Hodgdon’s Online Reloading Manual is a useful example because it is both widely used and transparent about its testing methods. In its Frequently Asked Questions, Hodgdon answers the question, “How is the data in this load guide acquired?” with the following summary:
- All testing is conducted in pressure and velocity test barrels, primarily according to SAAMI specifications and, in some cases, CIP standards.
- Chamber pressure is measured using a piezoelectric transducer and reported in pounds per square inch (psi).
- Velocity is measured at a distance of 15 feet from the muzzle.
Testing conducted under SAAMI or CIP protocols is industry standard and exactly what handloaders want to see. However, even within these standardized procedures, variation exists. In particular, SAAMI protocols allow a degree of latitude that can introduce measurable differences between test facilities, and those differences can influence published results.
SAAMI Test Protocol and Reference Ammunition
SAAMI testing is performed using specialized pressure and velocity barrels manufactured to tight tolerances. SAAMI specifies barrel length, chamber dimensions, bore diameter, rifling geometry, and the exact location of the conformal pressure transducer within the chamber.
To maintain consistency across the industry, SAAMI also employs reference ammunition. This ammunition is produced under tightly controlled conditions and distributed to multiple SAAMI-certified test laboratories as part of a round-robin testing process. Each facility measures pressure and velocity using its own equipment, and the results are reported back and averaged to establish baseline reference values.
These reference values allow individual ballistics laboratories to calibrate their equipment and verify that their measurements fall within an acceptable range. Under SAAMI guidelines, measured pressure is allowed to deviate by ±1,500 psi and velocity by ±25 feet per second from the reference ammunition values. Deviations within this range are considered normal, and applying correction factors is not mandatory.
Most laboratories choose to apply correction factors so their test setup aligns closely with the industry average. Some do not.
If test results fall outside the allowable tolerance range, corrections must be applied under SAAMI protocol. However, there is no clearly defined threshold at which a pressure and velocity barrel is automatically deemed unserviceable. Determining when a test barrel has reached the end of its useful life is typically left to the discretion of the individual test facility.
Barrel life varies significantly by application. Many pistol pressure barrels may remain serviceable for 50,000 rounds or more. In contrast, high-intensity rifle cartridges such as the 7mm Remington Ultra Magnum may wear a pressure barrel out in as few as 1,000 rounds.
What This Means for Published Load Data
So how does this affect the load data we see as handloaders?
In most cases, we do not know whether correction factors were applied to the published data. If one source applies a −1,000 psi and −15 fps correction while another publishes uncorrected results, the second source may appear to list a hotter load—even if every other variable is identical.
In practice, the data often shifts slightly to compensate. One source may list a marginally higher powder charge than another, typically differing by only a few tenths of a grain. Handloaders notice these discrepancies, and careful readers often conclude that the source listing the lower charge is the more conservative dataset.
That conclusion is not necessarily wrong—but it is incomplete without understanding how the data was generated.
CIP Testing Versus SAAMI Testing
While SAAMI and CIP exist for similar reasons, they employ different testing methodologies, chamber and cartridge specifications, and pressure standards.
SAAMI primarily relies on a conformal piezoelectric transducer that measures pressure indirectly through deformation of the cartridge case wall. CIP, by contrast, uses a drilled-case method in which a hole is drilled into the cartridge case. When chambered, this hole aligns directly beneath the pressure transducer, allowing the sensor to directly sample propellant gas pressure.
These two measurement methods alone can produce small but meaningful differences in recorded pressure. When combined with differences in chamber dimensions, throat geometry, and allowable service pressures, those differences can grow.
SAAMI and CIP often specify different maximum service pressures for the same cartridge. In some cases CIP limits are higher than SAAMI’s; in others they are lower. Depending on which organization’s standards are used, what constitutes a “maximum load” can legitimately differ.
Mixed or Unspecified Standards
Most test facilities do not develop load data using strictly SAAMI or CIP pressure-testing procedures. SAAMI and CIP protocols exist for only a limited number of standardized cartridges, relative to the vast number of wildcat and proprietary designs in circulation. In those cases, testing is performed using the best methods available to the laboratory, often employing a mix of pressure-measurement techniques.
Many companies do not publish pressure data at all. Instead, they publish velocity data alongside a maximum charge weight. The reader is left to assume that the listed maximum charge is based on some form of pressure evaluation—whether direct measurement using a piezoelectric transducer, indirect measurement via a strain gauge system, or inference based on traditional field indicators such as case head expansion and primer flattening. That last category is inherently subjective and far less repeatable than instrumented pressure measurement.
A Useful Illustration on Load Data
Hornady provides a useful illustration of this nuance and, to their credit, is unusually transparent about how their data is generated. In the 11th Edition of the Hornady Handbook of Cartridge Reloading, they describe their testing methodology as follows:
“When possible, loading data was fired in a special firearm designed to measure pressure. There is a description of a pressure gun in the Illustrated Glossary of the Hornady Handbook. The barrel and chamber dimensions are carefully produced to exact SAAMI specifications. Data is generated until a maximum pressure, determined by SAAMI, is reached. These various loads are then test fired in commercially available firearms for velocity. The powder charge and velocity chart in the Hornady Handbook were derived from these test firings.”
“In some calibers and for some cartridges, pressure barrels were not available. We developed and tested loads in these situations by employing a factory or custom firearm and by examining the brass case and the fired case extracted from the chamber. The brass case will show several indications of increasing pressure. One is case head expansion, as measured by a micrometer and compared to a fired factory-loaded cartridge. Other pressure signs of significance include cratered or flattened primers, brass flow into ejector slots, case head separation, and difficult extraction.”
“We employed the procedures above only when we have no other option. The vast majority of the data in this book was derived from the use of strain gauges.”
“All testing of this reloading data was done at 70 degrees Fahrenheit. Higher temperatures usually increase pressure and velocity. Lower temperatures generally result in lower pressure and velocity.”
There is a lot to digest in these statements, but several important conclusions can be drawn.
Key Takeaways from Hornady’s Methodology
- Pressure measurement methods vary
- Pressure may or may not have been established using a dedicated pressure barrel.
- The methodology does not explicitly state that SAAMI or CIP pressure protocols were followed in all cases.
- It cannot be assumed that a piezoelectric transducer was used for every pressure measurement.
- Velocity data may not directly correlate to pressure data
- Hornady indicates that pressure data and velocity data may be derived from different test platforms.
- Some data relies on traditional pressure indicators
- When pressure barrels were unavailable, Hornady relied on case head expansion and visual pressure signs such as flattened or cratered primers, brass flow, and difficult extraction.
- Strain gauge testing plays a significant role
- The majority of Hornady’s pressure data is derived from strain gauge testing.
The practical challenge for the handloader is that individual load tables often do not specify which testing methodology was used. Hornady does list the test firearm, barrel length, and twist rate for their load data. However, it is not always clear whether maximum load values were established in that firearm or in a separate pressure barrel, with the listed firearm used solely for velocity measurements.
This lack of clarity makes it difficult to assess how closely a given dataset aligns with established pressure standards for a cartridge and can lead to confusion when comparing one data source to another.
It is important to emphasize that Hornady is used here as an example, not as a criticism. Their testing and data presentation are broadly representative of industry practice and highlight systemic limitations rather than any specific shortcoming.
What This Means for the Handloader
In an ideal world, all handloading data would be generated using full SAAMI or CIP pressure-testing standards for every cartridge, bullet, and powder combination. In practice, that is neither realistic nor economically feasible.
Developing pressure-tested data is expensive. A dedicated pressure barrel can cost on the order of $1,000 per barrel, a SAAMI cartridge adapter may cost $3,000–$4,000, and that is before accounting for consumable components, instrumentation, labor, and range time. Expanding this process across the vast number of possible component combinations would quickly become prohibitive.
As a result, alternative pressure-measurement methods are commonly used. Strain gauge systems offer a significantly lower-cost means of estimating chamber pressure and are widely employed throughout the industry, including by Hornady. These systems are capable of producing useful and repeatable data, but they inherently introduce more variability than piezoelectric transducers used in dedicated pressure barrels.
The degree of variation depends heavily on how the strain gauge system is implemented. Results will differ depending on whether the gauge is applied to a tight-tolerance pressure barrel or to a commercially manufactured firearm, as well as how the system is calibrated and interpreted. Each of these factors influences the final pressure values reported.
None of this makes the data invalid—but it does explain why published load data from different sources may not agree, even when all parties involved are operating in good faith and using sound methodology.
What This Is Not About
The purpose of this discussion is not to cast doubt on the reliability or safety of published handloading data. Rather, it is to acknowledge that different load manuals can and do publish different data for what appear to be identical powders and bullets.
These differences are not always attributable solely to lot-to-lot variation in components such as powder or brass. They can also stem from real-world differences in test equipment, test platforms, and testing methodologies.
Handloaders inherently accept a degree of risk when they assemble their own ammunition. That risk is rarely a function of the published data itself and is far more often tied to how that data is applied. Problems most commonly arise from errors in the loading process or from intentionally exceeding published maximum charge weights in pursuit of higher velocity.
What Is Best Practice for Load Data?
The best practice in handloading is straightforward: begin with the bullet manufacturer’s published data. If you are loading a Hornady bullet, use the Hornady reloading manual. If you are loading a Barnes bullet, use Barnes’ data. Treat the bullet manufacturer as the primary source whenever possible.
In practice, most handloaders use bullets from multiple manufacturers and do not want to maintain a shelf full of loading manuals. In those cases, secondary sources are commonly used. The most typical secondary source is the powder manufacturer, which often publishes load data covering a wide range of bullet weights and constructions from multiple prominent bullet makers.
A third category of data comes from generalized manuals such as Modern Reloading by Richard Lee. This data is not considered “third” because it is less reliable, but because it is more generic in nature. These sources commonly list powder type and bullet weight or construction without always specifying a particular bullet manufacturer. This type of data fills an important gap, especially for bullets whose manufacturers do not publish load data of their own.
What handloaders should avoid is fixating on discrepancies between individual load manuals. There is too much potential variation in components, test equipment, and testing methodology to directly compare published numbers across sources. Load data represents a snapshot of how a specific combination of components performed under a specific set of conditions on a specific day. It is indicative of performance, not an absolute truth.
This is why the long-standing guidance within the handloading community has always been the same: start low and work up.
-Jay-
Revised 2/6/2026