Compatible powders: basic reloading is a simple science, but finding the ideal propellant for a given cartridge is worth the search

Guns Magazine, August, 2002 by Sam Fadala

Case capacity, shape and internal bore volume are three major factors that dictate which powder works best in a particular cartridge, along with a generous helping of alchemy and mystery. The latter surfaced one time when noted riflemaker Frank Wells lopped off a .270 barrel to see what effect it would have on powder performance. All the way down to 18 inches, H-4831 provided the best ballistics. Why not a faster-burning propellant, one that is consumed more readily as bore volume diminishes? The answer is blowing in the wind.

A similar situation developed recently with a .260 Remington in a stubbed-off barrel, which, to tell the truth, was too short, carrying ease notwithstanding. In spite of its flamethrower length, that .260 provided best ballistics with the relatively slow-burning IMR-4350 or H-4350 powders. Of course barrel length counts. This is not to suggest that internal barrel volume is not a significant factor in powder selection. A snubnose .38 dies with a slow-burning rifle powder. But tube length alone doesn't dictate the best powder choice.

Deciding Factors

Matching the right powder with a specific cartridge, bullet and gun has two major goals: accuracy and raw ballistics, along with safe working pressures, of course. Case capacity is an obvious factor. Magnum bottles with large fuel capacity do better with slower-burning propellants. Diminutive cases require faster-consuming powders.

Today, we're rich in both choices. Cartridges that never realized their initial potential are rockets with some of the newest powder numbers. The .300 Winchester Magnum comes to mind with H-1000 pushing a 180-grain bullet close to 3,200 fps muzzle velocity from a 24-inch barrel. There are also some good propellants that have been around for a while, but which are only now finding their way onto the shelves of grassroots handloaders. I'm thinking of IMR-7828. My own 7mm Remington Magnum spits out 160-grain bullets at 3,200 fps with heavy charges of IMR-7828. The first time this high figure registered on the chronograph, I thought it must certainly be an error. Retesting proved that there was no mistake.

Case shape is another matter. Short and fat are "in" today for two reasons. First, squat cartridges tend to be accurate, as shown by rounds such as the 6mm PPC and the ever-popular .308 Winchester, perhaps the most accurate .30-caliber cartridge commercially available today. Second, short and fat means extra powder capacity per cartridge length, which translates into more capacity in a standard length or shorter action.

The .284 Winchester is a perfect example. This neglected cartridge has a rebated rim and a fat body. Although case length is only 2.17 inches, compared with the .30-'06 Springfield at 2.494 inches, case capacity is about the same. On the other hand, shape can be over-credited. If this were not true, slope-shouldered rounds such as the 1920's vintage .300 H&H, as well as old-timers like the .32-40 Winchester and .38-55, would not shine, which they do. The last two produce fine accuracy, while the .300 H&H remains powerful to this day, no stranger to 3,000 fps with a 180-grain bullet. Also impressive is Ben Comfort having won the 1,000-yard Wimbledon Cup with a .300 H&H Enfield rifle at Camp Perry in 1935. The next year, Winchester began chambering rifles for the English round.

Regardless of these facts, the squat cases that are currently so popular do have a penchant for accuracy. Furthermore, case shape does have something to do with how powder bums. If this were not so, my own .25-284 Winchester wildcat would never develop higher velocity than the .25-'06 Remington, and the chronograph proves that it does.

Shooting Is The Proof

The only method I know of to determine compatible powders is shooting. Nothing from scientific formulas to reading tea leaves can take the place of trial and error at the range for both bullet speed and accuracy in a specific firearm. This past hunting season, I carried a Marlin Model 336A .30-30, the 24-inch barrel providing a flat 2,400 fps with a 165-grain Swift A-Frame bullet. The .30-30 does well with a long string of different powders, but Reloder 15 rang the bell. At 50 yards, groups under an inch were commonplace, with some running much smaller. And this was done with a Lyman aperture sight, not a scope.

I gathered up a mule deer and two white-tails with the Marlin, plus a fine antelope buck with a hundred-year-old Savage .30-30 firing a 150-grain bullet. While not up to the push of the .308 Winchester by any means, the old treinta y treinta, as it's known in Mexico, licked flames on the heels of the factory loaded .300 Savage, and that's not bad. Success was born of finding the right powder for that old round. Meanwhile, the same Reloder 15 powder propelled a 165-grain bullet at 2,600 fps in the Roaring Twenties vintage .300 Savage cartridge, while the T65 7.62 NATO, better known as the .308 Winchester, reached 2,800 fps with Reloder 15 and a 165-grain missile.

The aforementioned .25-284 wildcat also liked a particular Reloder powder, Number 19. A velocity of 3,400 fps was proved over and over with a 100-grain bullet from the 22-inch Morrison Precision barrel. Groups under half an inch were commonplace at 100 yards.