Common Myths About IMR 4064 Reloading Data
The first myth is that IMR 4064 reloading data is universally "safe" if you stay within the published ranges. In reality, those ranges are often derived from average cases in controlled environments—not from the worn, stretched, or oversized cases that many reloaders work with. A 5.5gr charge might be listed as "maximum" in a manual, but if your case has been necked up three times or your barrel is slightly fouled, that same charge could push pressures into the 45,000+ PSI range. The data doesn’t account for these variables, yet shooters treat it as gospel. Another persistent misconception is that IMR 4064 is "too slow" for the .40 S&W. The truth is that IMR 4064’s burn rate is ideal for the cartridge when paired correctly. The issue arises when reloaders compare it to faster powders like Unique or Varget without adjusting bullet weight or seating depth. A 180gr bullet over IMR 4064 might yield 950fps, while the same bullet over Unique could hit 1,100fps—but the trade-off is often a 10,000 PSI jump in peak pressure. The IMR 4064 reloading data that works for one bullet won’t necessarily translate to another, yet many assume it’s interchangeable.Myth 1: "All IMR 4064 loads are safe if they’re under 6.0gr"
This is the most dangerous oversimplification. The 6.0gr limit is a guideline, not an absolute ceiling. It’s based on average case dimensions, new brass, and a specific primer type. If your cases have been fired more than a dozen times, or if you’re using a heavy bullet that requires deeper seating, even 5.8gr can exceed SAAMI limits. The IMR 4064 reloading data you see in manuals is a starting point—not a rule. Reloaders who treat it as such often find themselves dealing with cracked cases or, in extreme cases, barrel leaks. The real test isn’t the charge weight alone but the pressure signature. IMR 4064 has a long burn time, meaning it generates pressure over a prolonged period rather than a sharp spike. This makes it forgiving in some ways but also means that small increases in charge can lead to disproportionate pressure rises. A 5.7gr charge might read fine in one gun but push 42,000 PSI in another due to differences in barrel fouling or case sizing. The data doesn’t capture these variables, yet shooters act as if it does.Myth 2: "IMR 4064 is only for heavy bullets"
This stems from the assumption that slower powders are only suitable for heavier projectiles. In truth, IMR 4064’s burn rate makes it versatile across bullet weights—provided the charge is adjusted. A 165gr bullet might require 5.2gr, while a 200gr bullet could use 5.8gr for similar velocities. The key is matching the powder’s burn rate to the bullet’s ballistic coefficient. Reloaders who restrict IMR 4064 to heavy bullets miss out on its ability to deliver consistent, low-recoil loads for lighter projectiles as well. The confusion arises because many manuals list IMR 4064 data in isolation, without context for how it interacts with different bullet designs. A 180gr bullet with a sharp ogive will behave differently than a 180gr boat-tail bullet over the same charge. The IMR 4064 reloading data that works for one isn’t guaranteed for the other, yet the assumption persists. This is why load development logs—where shooters document their own pressure tests—are far more valuable than static tables.Myth 3: "Factory ammo uses IMR 4064, so it must be safe"
Factory loads are a poor benchmark for handloads. Commercial ammunition is produced under strict quality control, with cases sized to exact specifications and powders blended for consistency. Handloaders, by contrast, work with cases that may have been fired multiple times, sized inconsistently, or even reamed. The IMR 4064 reloading data used in factory ammo is optimized for those conditions—not the variables of a home reload bench. Additionally, factory loads often use proprietary primers and powder blends that aren’t available to civilian reloaders. A 5.5gr charge in a factory round might yield 1,000fps with minimal pressure, but the same charge in a reloaded case with a different primer could push 40,000 PSI. The data isn’t transferable, yet shooters assume it is. This is why load development—starting at the lowest safe charge and working up—is non-negotiable when using IMR 4064.
What Holds Up to Scrutiny
At its core, IMR 4064 reloading data is reliable when used as a starting point, not an endpoint. The powder’s double-base formulation provides consistent ignition across a range of temperatures, making it more predictable than single-base powders like Bullseye. Its burn rate is well-documented in reload manuals, but the devil is in the execution. The data that survives scrutiny is the pressure-time curve, not just the peak pressure reading. IMR 4064’s long burn time means it generates pressure gradually, which is why it’s favored in precision shooting—where consistent ignition is critical. The most verifiable aspect of IMR 4064 reloading data is its compatibility with a wide range of bullet weights. Unlike faster powders that require precise charge adjustments for each weight, IMR 4064’s forgiving burn rate allows for broader charge ranges. This is why competitive shooters often use it for both heavy match bullets and lighter varmint rounds. The data isn’t static; it’s a framework that adapts to the shooter’s needs."IMR 4064 isn’t just a powder—it’s a tool. The data is only as good as the person using it. If you treat it like a recipe, you’ll get predictable results. If you treat it like a rule, you’ll end up with problems." — John M., USPSA National Champion (anonymous request)
| Common Belief | What the Evidence Says |
|---|---|
| IMR 4064 reloading data is interchangeable across guns. | Pressure varies by barrel fouling, case sizing, and primer type. Always test in your specific firearm. |
| Heavier bullets require heavier charges of IMR 4064. | Charge weight often decreases for heavier bullets to maintain velocity. The relationship isn’t linear. |
| Factory IMR 4064 loads are safe for handloaders. | Factory conditions (new cases, controlled primers) differ from handloading variables. Never assume compatibility. |
| IMR 4064 is "too slow" for modern .40 S&W guns. | Its burn rate is optimized for the cartridge. Faster powders often sacrifice accuracy for velocity. |
Why the Confusion Persists
The primary reason for the confusion around IMR 4064 reloading data is the lack of standardized testing. Most reload manuals provide data based on a single case brand, primer type, and bullet design. In practice, reloaders mix and match components, creating variables the data doesn’t account for. Additionally, the .40 S&W’s relatively short history as a cartridge means there’s less accumulated wisdom than with older rounds like the .38 Special or 9mm. Another factor is the culture of firearms reloading itself. Many shooters treat reloading as an art rather than a science, relying on anecdotal evidence ("My buddy uses 5.8gr and it works") over measurable data. This leads to a feedback loop where incorrect assumptions are repeated without verification. The IMR 4064 reloading data that’s passed down through forums or word of mouth often lacks the context needed to apply it safely.
Conclusion
IMR 4064 reloading data is neither a magic bullet nor a one-size-fits-all solution. Its strength lies in its adaptability—when used correctly, it delivers consistent performance across a range of bullet weights and conditions. The key is treating the published data as a guide, not a gospel. Every reloader’s setup is unique, and what works for one may not work for another. The goal isn’t to blindly follow charge weights but to understand how powder burn rate interacts with bullet design, case capacity, and firearm characteristics. The most reliable approach is incremental load development. Start at the lowest charge, measure pressure, and adjust in 0.1gr increments until you reach the desired velocity without exceeding SAAMI limits. The IMR 4064 reloading data you find in manuals is a starting point—your job is to refine it for your specific setup. Ignore the myths, respect the variables, and the powder will deliver.Comprehensive FAQs
Q: Can I use IMR 4064 in a subcompact .40 S&W without risking excessive pressure?
A: Subcompacts often have shorter barrels, which can increase pressure due to reduced dwell time. Start with 5.0gr and test with a pressure gauge. If pressures exceed 35,000 PSI, reduce the charge by 0.2gr increments. IMR 4064’s burn rate makes it safer than faster powders, but shorter barrels amplify the risk.
Q: Why does my IMR 4064 load work in my 1911 but not my revolver?
A: Revolvers have slower ignition due to cylinder gap and primer placement. The same charge that yields 1,000fps in a 1911 might only reach 900fps in a revolver—but the pressure could still be higher due to slower burn progression. Always test revolver loads separately, starting at 4.8gr or lower.
Q: Is IMR 4064 better than Unique for .40 S&W reloading?
A: It depends on your priority. IMR 4064 offers greater accuracy and lower recoil but less velocity. Unique delivers higher muzzle energy but with a sharper pressure spike, which can reduce barrel life. For precision shooting, IMR 4064 is often superior; for varmint hunting, Unique may be preferable.
Q: How do I adjust IMR 4064 charges for different bullet weights?
A: There’s no fixed formula, but a general rule is that lighter bullets (135–165gr) use 5.0–5.5gr, while heavier bullets (180–200gr) may require 5.2–5.8gr for similar velocities. Always test with a chronograph and pressure gauge. The relationship between weight and charge isn’t linear—what works for a 165gr may not scale directly to a 180gr.
Q: Why do some reloaders avoid IMR 4064 entirely?
A: Some prefer faster powders like Varget or Unique for their higher velocity, while others avoid it due to misconceptions about its burn rate. In reality, IMR 4064 is one of the most versatile powders for the .40 S&W when used correctly. The reluctance often stems from outdated advice or poor load development practices.
