Powder: the push behind the bullet: The size, shape and makeup of each grain controls burn rate, pressure, accuracy. Here’s what’s to know.
Though ancient Chinese get credit for crude explosives, gunpowder was first described by Roger Bacon in 1249. The English Friar may not have considered its place in weapons; but crude firearms soon took shape. From the 14th century to the late 19th, black powder supplied the high-pressure gas that hurled all manner of projectiles. A blend of fuels and oxidants, black powder comprised various blends of sulfur, charcoal and saltpeter. In 1846 Ascanio Subrero in Italy discovered nitroglycerine, which yielded more oomph. A clear, oxygen-rich solution of nitric and sulfuric acids plus glycerin, “nitro” eagerly rearranges itself into stable gases. No need for spark; a jolt can start the process. In 1863 Swedish chemist Emmanuel Nobel and his son Alfred learned how to put this touchy compound in cans. Still, it proved rambunctious. After it demolished Nobel’s German factory, Alfred came up with Dynamite in 1875.
By then Swiss chemist Christian Schoenbein had found that cotton treated with sulfuric and nitric acids burned so fast, it became ash without igniting black powder beneath it! Alas, John Hall’s guncotton plant in Faversham, England blew up. So did German immigrant Carl Dittmar’s New Sporting Powder factory, flattening much of Binghampton, New York.
Nitrocellulose-based smokeless powders replaced black in firearms in the 1890s. These “single-base” propellants include England’s “cordite,” named for its spaghetti-like strands. Adding nitroglycerin yields double-base powders, which pack more energy per grain. DuPont powder guru Larry Werner told me: “To get nitro’s full effect, you need about 10 percent in the mix. Double-base powders are especially useful in cases of limited capacity. Spherical powders are double-base. Their drawback is residue. They don’t burn as clean as single-base.”
Nearly all smokeless powders have a stabilizer like diphenylamine to extend shelf life. A flame retardant reduces muzzle flash. Graphite coatings that impart gray color help ward off static electricity.
Formulated for military use, early DuPont smokeless powders sold in cans marked “MR.” A line of IMR (improved military rifle) powders arrived in the 1920s, when four-digit DuPont numbers replaced two-digit, beginning with 4198. In 1934 DuPont introduced IMR 4227. Shortly, IMR 4895 would fuel the .30-06 in the M1 Garand. IMR 4831, for 20mm cannons, would become popular for magnum rifle rounds.
Huge stocks of powder had been dumped at sea after World War I. Brewster E. Hodgdon, serving the Navy in the 1940s, had a better idea. He would buy surplus powder, then peddle it to handloaders like himself. He borrowed against his life insurance to get 25 tons of 4895 and stored it in a boxcar in a rented field. Customers drawn by an ad in American Rifleman got 150 pounds for $30! Sons J.B. and Bob crated it and took it to REA and Merriam Frisco terminals in a 1940 Ford. Tons of 4831 followed. Brisk demand led to formation of the Hodgdon Powder Co. in 1966. Magazines appeared on 160 acres west of company headquarters in Overland Park, Kansas. Bruce Hodgdon would sell four million pounds of powder!
By 1959, surplus powder stocks had diminished. Among commercial sources Hodgdon tapped to fill orders was a plant in Scotland that supplied British armed forces. Hodgdon bought spherical powder, pioneered by John Olin in ‘33, from the Olin Corp. (“Ball Powder” is Winchester’s trade-marked name.) Decades later, Hodgdon sells Winchester canister powders under a licensing agreement. DuPont wouldn’t release extruded powders to Hodgdon in the 1960s. Ironically, it later sold Hodgdon its powder business! Hodgdon distributes Vihtavuori propellants too. While it doesn’t manufacture powder, Hodgdon employs chemists to develop new types. It now markets more than 120, accounting for 70 percent of rifle, handgun and shotgun powders sold to consumers.
Powder numbers have nothing to do with burning rate. After his career at Hodgdon, Ron Reiber told me WC852 powder got a new name when Bruce tried it in his .22-250. “He used 38 grains to start 50-grain bullets at 3,800 fps. That powder became H380.” Larry Werner, whose DuPont tenure dated to the 1950s, said that company labeled propellants chronologically. Low numbers are early types.
“Closed bomb” tests measure burn rate. A specific powder ignited in a chamber of known volume yields a distinctive pressure curve. But the real-world behavior of a powder hinges on case capacity, bore diameter and bullet weight. Werner told me IMR powders were given Relative Quickness values. “IMR 4350 had an RQ of 100, faster IMR 4227 an RQ of 180. IMR 4198 came in at 165, IMR 3031 at 135.”
Fast-burning propellants are suited to small, wide-mouthed cases and short, light bullets. A quick thrust behind a long, heavy bullet can’t easily overcome its substantial bore friction and mass. Pressures spike. That bullet needs a more gradual nudge, the sustained push of slow-burning powder. A pistol bullet has less bearing surface for its diameter. Its big base spreads pressure. A generous bore offers gas a broad cavity that grows behind the moving bullet. Slow powder will disappoint, as the bullet outruns expanding gas. A short barrel dumps thrust before slow powder can transfer even half its energy.
Grain shape affects gas release as powder burns. Grains of flake and spherical powders shrink; so they burn regressively. Extruded or “stick” powders are tubes. While flame consumes the outer surface of each tube, the central hole grows in surface area as it burns. Extruded grains may have multiple holes so they burn progressively. Burn that expands each hole’s interior more than offsets shrinkage outside. Until all holes burn through, grain surface area increases as the powder is consumed.
“Extruded powders are usually more consistent over temperature ranges than spherical powders,” Chris Hodgdon explained, adding that extruded powders are intuitively best for sustained thrust in fixed-breech rifles. But spherical powders can work in this arena too. Additives take the place of grain structure to throttle burn rate and gas release. Gas-driven self-loading rifles work best with powders near mid-rate in the charts. Pressure curves must match rifle design, to ensure the proper thrust at the barrel port.
Handloaders have long debated differences in burn rate between IMR and Hodgdon powders of the same number. Hodgdon bought the IMR line in 2003, after selling its “H”-prefix powders for decades. Differences in blending distinguish H4831 and IMR 4831. Same goes for 4350 and a few others. “Load data for H4831 and IMR 4831 differ,” Chris Hodgdon affirmed. “When not specified in a manual, assume the powder is IMR.” The same applies to other extruded powders labeled Hodgdon and IMR. In magnum cases, with charges of 70 to 80 grains, I’ve found IMR 4831 a tad faster than H4831, traditional and short-cut. IMR 4227 and H4227 are essentially identical.
While many useful propellants date to the military-surplus era that put 30 pounds of H4831 in my loading room, new powders offer advantages like cleaner burn, better metering, less sensitivity to changes in temperature. Hodgdon’s Extreme line, introduced with Varget in 1996, delivers uniform performance across a wide temperature range. Hodgdon also markets Superformance and LEVERevolution powders derived from Hornady’s work with high-octane loads for specific cartridge classes.
Before handloading powder that has aged, you’re smart to examine it in hand. Red dust indicates deterioration from improper storage or flawed production. “Rusty” powder is best flushed down the toilet. To prolong the life of powder, keep it capped in its original container in a dry, cool (not freezing!) place.
Physically, powder comprises grains, as does a pail of sand. Powder charges are given in grains weight – entirely different. There are 437 ½ grains per ounce, 7,000 grains per pound. The measure dates to the Bronze Age, when the weight of a grain of wheat had legal standing. Black powder is measured for muzzle-loading rifles by bulk (a teaspoon is a bulk measure). But the adjustable tube that dumps powder into the barrel is pre-set by the shooter to hold a given weight of powder when filled. So grains weight is still what matters.
Handloading manuals by bullet and powder manufacturers show starting and maximum charges. “High volume shooters” who use progressive presses rely on powder dispensers to throw uniform charges of spherical and small-grain stick powders. (Coarse stick powders for magnum loads do not meter well). Hunters typically hand-weigh every charge. Balance-beam and electronic scales yield .1-grain precision.
Ideally, a powder column should fill a case to the base of the seated bullet. Dead space in a case allows powder to shift, which can affect its behavior. Reduced charges of slow powders in big cases have caused pressure spikes. Speculation has it these are caused by primer flame skating across the horizontal powder surface to ignite the front of the charge as it ignites the rear. The burn then speeds from both ends to a violent finish, mid-case. Inert filler can be used atop powder in reduced loads.
While compressing a powder column with the bullet causes no harm, crushing grains by jamming a bullet deep into a tall charge can affect burn rate and pressures. The press of the powder can even cause bullet creep in the rifle’s magazine during recoil. Spherical powders, like marbles, don’t compress well.
To get the most powder into a case, pour it slowly, tipping and tapping the case on its rim as you rotate it. A drop tube dribbles a thin stream that lets grains jostle for space.
Practical advice for new handloaders: Start at 5 to 10 percent below maximum charges. Load and fire three rounds, minding signs of high pressure: hard extraction, flattened primers, ejector marks on case heads. Detecting none, boost charges in small increments to get desired velocity and accuracy.
Consistent increases in velocity on a ladder of stiffer loads can lull you into thinking that for each additional grain of powder you’ll get, say, another 50 fps, and pressures will climb apace. Not so! Every propellant behaves in its own way to changes in charge weights in specific cases. Velocities can “plateau” – and pressures can spike – as charges near case capacity. In one .35 wildcat, I got about 30 fps per added grain of RL-19, while RL-22 yielded 22 fps/grain. But 3 grains of H1000 bumped velocity 180 fps: 60 per grain! I got a similar rate of increase from Accurate 3100, while H4831 behaved more like RL-19. These powders are very closer in burn rate.
The behavior of handloads, and appearance of fired cases, can mislead. Muzzle flash may seem to signal too much powder; in fact, it’s most common in low-pressure loads. Blackened case necks also tell of anemic loads: They lack pressure to seal the case neck against the chamber.
Whichever powder you use, or how much, only about a 30 percent of its energy will actually push the bullet. About that amount is lost as heat inside the case and barrel. Nearly 40 percent becomes useless exhaust at the muzzle!
Myriad powders are currently peddled under the banners of Accurate, Hodgdon, IMR and Norma, Reloder (Alliant, Hercules), Vihtavuori, Western (Ramshot) and Winchester. A top source for powder and other handloading components – and the tools and manuals to use them – is Midsouth Shooters Supply.