Compressed charges of gunpowder can result in best-possible performance, but it’s necessary to understand the potential downsides before working up a compressed load. (Photo courtesy of Joseph von Benedikt)
February 27, 2025
By Joseph von Benedikt
Compressed propellant charges in your handloads can be good, bad or ugly. A compressed charge is basically exactly what it sounds like. There’s more gunpowder than there is room inside the cartridge case once the bullet is seated. The act of seating the bullet in the case neck compresses the gunpowder down into the case.
Let’s start with the benefits of compressed loads, and then address the disadvantages. You’ll find some rules of thumb for loading compressed charges in the accompanying sidebar.
Compressed powder granules are held securely in place, and there’s no empty space inside the case. According to Hornady ballistician Jayden Quinlan, eliminating propellant ullage (free space in the cartridge case) is particularly helpful when shooting up or down at steep angles. Compression keeps the propellant from shifting forward or rearward as the rifle is aimed steeply down or up. That means it always ignites consistently.
Even when shooting on level ground, a lightly compressed powder charge will usually provide more consistent velocity than a powder charge that only partially fills the case. When there’s a lot of empty space inside a cartridge case, the primer flash sometimes does not penetrate and permeate the gunpowder as effectively, resulting in less consistent velocity.
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The Science Two shooters test out compressed loads at their local shooting range. To visualize why, imagine a mesh bag filled with dry autumn leaves being hit with a blast from a propane flame-thrower. The leaves represent gunpowder granules, and the flame-thrower the primer flash. They’re contained, and the blast ignites them nearly instantaneously. Now imagine those same leaves in a loose pile. Blast them with the flame-thrower, and half of them will dance out of the way without catching alight.
“We generally achieve impressive results with compressed loads,” Barnes Bullets R&D supervisor Gregg Sloan told me. “As long as we are operating within safe pressure limits, we have measured and seen more consistent velocity and pressure, meaning lower standard deviation and extreme spread on both.”
Here’s an advantage that mostly applies to heavy-recoiling cartridges. When the base of a bullet is sitting on a compressed propellant charge, it’s very unlikely to “set back”—a phenomenon that sometimes occurs when a cartridge in the magazine takes several thumps on the nose of the bullet caused by recoil. This can make the bullet migrate down into the cartridge case.
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Set-back can also occur when a cartridge is aggressively chambered. When the nose of the bullet slams into a steep feed ramp, it can push the bullet back into the case—slightly or significantly.
Advantages and Disadvantages Both of these situations can cause malfunctions. That’s why, particularly with big-bore cartridges often used on dangerous game, eliminating set-back can be such a significant advantage that ammunition is intentionally loaded with compressed charges.
“Compressed charges are sometimes used—especially in large dangerous game loads—to create very high-quality ammunition,” Nosler’s Mike Lake said.
Compressed charges can also lead to increased velocity. For instance, slow-burning propellants ideal for magnum rifle cartridges are way below maximum when the charge reaches 100 percent fill. Consistency is probably good, but velocity still leaves something to be desired. Adding powder to the point of compression can bring velocities up to snuff.
Accuracy often increases with a lightly compressed load as well.
Accuracy Increase? “We have seen good accuracy results in many loads that would be considered compressed, and have many times achieved an improvement when compared to the same set of components at a lower case fill and charge,” Sloan said.
But compressing charges isn’t always a bed of roses.
“Compressing propellant in a cartridge case too much can have different adverse effects with a range of severity,” Quinlan said. “The least consequential could be damage to the bullet while seating. The additional compression of the propellant may leave scuffs, rings or gouges in the ogive of the bullet during seating and could have a negative aerodynamic effect.”
Quinlan also cautioned against compressing propellant to the point where you cause cracking or breaking of the powder granules. This changes the grain structure and can alter the burn rate characteristics. The result? Potentially higher pressures.
The Risk of Higher Pressures “Although not common, it is possible,” Quinlan said. “Increased muzzle velocity variation or increased dispersion could also be observed with too compressed of a load.”
According to Steve Faintich, Hodgdon’s vice president of research and development, the two main drawbacks of a compressed load are ignition and cleanliness of burn. “Modern smokeless rifle propellants are designed to include air in the case to provide oxygen for ignition,” he said. “When you compress the propellant, you squeeze the air out of the case and make for more inconsistent ignition. Also, the additional propellant may not completely ignite, which could cause residue in the barrel.”
Compression can also lead to difficulty in seating bullets. In some cases you can’t get to the desired seating depth because the compressed powder won’t allow the bullet to go deeply enough. Attempting to push past a certain point can cause the case to distort or bulge, and as Quinlan and Lake both noted, the bullet itself can distort. Both are bad. Lake also noted that even a single powder kernel wedged in by a long-taper bullet boattail can distort the case neck. This can prevent a cartridge from chambering.
Another issue that can come from higher case fill and compressed loads is inconsistent overall length. Too much propellant compression can actually cause loaded bullets to migrate outward from the case over time, leading to variation in overall lengths.
Rules of Thumb Don’t exceed more than five percent compression, also calculated as 105 percent case fill. Stick (extruded) powders compress more easily than ball (spherical) powders because there is more room between the kernels of stick powders. Powder choice is not set in stone, though. Some engineers consider spherical powders more suitable for compressed loads because their grain structure is less likely to fracture or fragment. While slightly compressing a load will not raise pressures, the wrong combination of adding more powder and seating more deeply that reduces case capacity will raise pressures. “Very generally speaking, if a load is aggressively compressed, you are working with the wrong powder for that particular cartridge/bullet combination,” Nosler’s Mike Lake said. If you’re going to go with a compressed load, follow reloading data exactly to avoid ignition problems or unsafe pressures. Always use data from reputable sources.
