Often, trying a different type of powder results in better accuracy than trying a bunch of different charge weights with one propellant. For instance, an extruded powder (l.) may prove to work better than a spherical one. (Photo submitted by the author)
October 17, 2024
By Joseph von Benedikt
“Try Reloder 19,” the ballistician told the range tech who had just fired a 1.5-inch 100-yard group with my semi-custom 7mm WSM. Clearly, the initial charge of H4831sc didn’t produce good accuracy with the Barnes 145-grain LRX, but switching powders after just one three-shot test group seemed a bit extreme to me.
The tech charged three of the short magnum cases with a starting load of Reloder 19. He fired a shot, then another. The second overlapped the first, and the third shot created a half-m.o.a. cloverleaf.
“Yep, it likes 19 better,” the ballistician said with a grin.
The range tech proceeded to find out whether the group was repeatable, and nine more rounds downrange created three more half-m.o.a. groups. I was convinced. If it had been me, I would’ve tried a bunch of different charge weights before switching, but the ballistician said a particular rifle often won’t like a certain type of powder—and you’re betting off switching to another type instead of chasing charge weights.
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Eye-Opening Results This experience occurred a decade ago, and was eye-opening for me. For much of my life, I’d planned my handloads according to what powder I had on hand and what was readily available. My favorite .30-06 Springfield, .280 Ackley Improved and .270 Win. handloads all used H4831sc. My go-to propellant for 7mm Rem. Mag. and .300 Win. Mag. was H1000. For high-horsepower magnums such as the .300 Wby. Mag., Reloder 22 was a favorite. If it’s not broke, don’t fix it, right?
Not necessarily. Having a broad selection of propellants on hand can make handload development much easier, rather than complicating it. So why do rifles prefer some propellants over others? And how does one determine the best to use in a given barrel?
The answer to the first question is challenging to answer. There are trends, rules of thumb and some useful probabilities, but scientific predictions are elusive.
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As Barnes’ lead ballistician Gregg Sloane noted: “When comparing a selection of proper burn rate powders for a given cartridge and bullet weight, I can’t really explain the ‘why’ behind a certain powder achieving better accuracy in a given gun over another. There are many factors to consider; slight changes of case fill, velocity consistency, and how the powder burns all play a role. Time to peak pressure, flame temperature, energy and pressure changes, and engraving force, among others.
The Rifle Will Let You Know “The effect of barrel harmonics and how one powder burns over another is an interesting thing,” he added. “It’s not easily measured and is hard to quantify.”
Actually determining which propellant is best in a given rifle is easier than predicting it, although it requires legwork. It’s all about testing. But first, a little background on the powders themselves.
Generally speaking, extruded or “stick” propellants—meaning the granules are long and cylindrical—provide slightly better accuracy than spherical or “ball” powders—meaning the granules are round or flattened/round shapes. There are lots of exceptions to this generality, though, so never write off spherical powders in your search for accuracy.
Extruded powders also tend to provide more consistent velocities. This may be a function of their tendency to stack in a more open column, allowing the flame from the primer to penetrate and permeate more immediately and evenly, resulting in a more consistent ignition and burn. Spherical powders can clump up, and those clumps are slower to burn, introducing inconsistencies.
Burn Rates Burn rates play a role as well. Within the appropriate burn-rate spectrum suitable for a given cartridge, propellants on the slower-burning end generally provide the most velocity, particularly with heavy-for-caliber bullets. However, faster-burning powders often provide slightly better accuracy. This is one of those hard-to-explain characteristics of gunpowder. The good news is we don’t have to understand it to benefit from it: If you have a rifle that’s proving stubborn about accuracy, try a faster-burning powder. You might be surprised.
The ideal powder charge is one that’s slightly compressed by the base of the bullet. This ensures that the propellant won’t shift away from the blast of the primer, enabling instant and consistent ignition. It also prevents the powder from lying in various different positions inside the case from shot to shot—something common in handloads with a lot of air space inside.
Although this isn’t a direct predictor of accuracy, it is usually a predictor of velocity consistency. A full or nearly full handload typically provides tighter extreme spreads and standard deviations than one with a high percent of air inside.
Some reloading manuals, such as Nosler’s, provide case-fill density in percentage by volume with their data. This can be valuable information, but it does vary a bit depending on cartridge case brand. And it can vary a lot depending on how deeply you seat your bullets.
Case Fill You can use those published case-fill density percentages to choose a propellant that should provide complete or nearly complete fill with your bullet. This is one scientific step that will provide predictable results.
Now, on to testing. When you begin load workup using a certain projectile in a certain rifle, be flexible in the powder you use. Pick a few propellants to start with, basing your decisions on case-fill density, burn rate and granule type. If you’re doing high-volume loading, pick spherical powders that meter easily; if not, start with extruded-type powders likely to provide best possible accuracy. If your first few groups aren’t promising, don’t be stubborn. Switch powders. Gun writer Wayne van Zwoll once told me that if a certain load shoots a bad group once, it’ll shoot a bad group again—maybe not every time, but even occasionally isn’t acceptable. “Why waste time trying to prove it won’t?” he said.
If accuracy proves elusive, try powders that are bulky but sort of fast-burning for the cartridge you’re working with. Keep switching until you find a propellant that produces significantly smaller groups than most. Optimally you’ll only go through two or three powder types before finding something your rifle responds well to. In extreme cases, you may need to try five or six. And yes, that can be a challenge in today’s era of starved supply lines.
On the plus side, you can do a lot of touch-and-go testing with one pound each of a handful of good propellants. Watch the shelves of local shops, and put together a collection of good powders suitable for the types of cartridges you usually load. I’ll wager you’ll use less powder, cause less barrel wear and achieve better accuracy by quickly trying a variety of powder types than you will by stubbornly working through a bunch of charge weight increments with just one type of propellant.
