January 04, 2011
By Lane Pearce
By Lane Pearce
These Hodgdon propellants are best suited for fastest and slowest handgun (9mm and .454 Casull) and rifle (.223 Rem. and .300 RUM) cartridges.
There are more than a hundred different propellants readily available for just about any application one could imagine. If you don't believe me, take a look at the burn-rate chart on page 2. So how do you select the best one from so many choices?
Well, I'm not aware of an obvious or precise method, but experienced handloaders know that a propellant's burn rate significantly affects cartridge performance. We also know that other factors also affect how fast or slow the burn rate is manifested in a specific cartridge/bullet/powder/primer combination.
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Generally, there are two types of propellant chemistry available to handloaders. Single-base powders contain primarily nitrocellulose with various coatings added to enhance stability and control muzzle flash and burn rate, etc. For example, most IMR and Hodgdon cylindrical or stick propellants are single-base.
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Double-base propellant is comprised mostly of nitrocellulose but also has another potent ingredient (nitroglycerine) added to increase the available energy. While most double-base propellants are spherical (ball) or flake powders, other brands offer double-base cylindrical powders.
As you might expect, the physical shape of each propellant granule significantly affects its burn rate. Stick propellants may be short and relatively fat or long and skinny, while others are both long and large in diameter. If you examine them closely, you'll see one or more perforation extending through each granule. On the other hand, ball powders can look like miniature, uniformly sized ball bearings or a mix of larger- and smaller-diameter granules, some of which are almost round, and others are flattened or even irregularly shaped. Flake powder is typically coarsely cut and bulky (i.e., less dense) compared to stick or ball propellants.
Burn rate is significantly affected by the granules' total surface area exposed to the initial primer flash. In addition, propellants are typically coated with chemical deterrents to delay--as the term suggests--and control burn rate. Therefore, for equal powder-charge weights, there is more or less surface area to ignite, depending on the quantity and configuration of the powder granules.
Typically, the maximum surface area exists at ignition, and it decreases during the few milliseconds the propellant burns. That's why the chamber pressure peaks almost immediately and then drops off rapidly. But other nonpropellant factors interact to determine a specific propellant's relative burn rate. These include case capacity and shape, expansion ratio (i.e., the bore volume compared to the chamber volume), bullet construction and weight, the specific industry pressure standards, primer brisance, and so on.
Large-capacity, magnum-rifle cartridges yield maximum velocities and energy with heavy charge weights of relatively slow-burn-rate powder. My .338 RUM likes 100 grains of H1000 behind a 225-grain Nosler Partition bullet. It takes a Large Rifle Magnum primer to reliably light this much powder.
At the other end of the cartridge scale, 2.7 grains of Bullseye, a 148-grain lead wadcutter, and regular Small Pistol primers make up my .38 Special target ammo. For this application, the light charge of fast propellant provides excellent results.
Second only to safety, achieving the desired performance from your handloads is the key objective. The .38 Spl. is a poor choice for shooting elk across a windy canyon. And punching holes in paper targets at 7 yards with the .338 RUM at the local shooting range is quite over the top.
Light charge weights of fast-burn-rate propellants are loaded in small, lower-pressure, straight-walled cartridges. Heavy charges of slow powder go in large, bottlenecked, higher-pressure rounds. As the cartridge capacity increases and/or the SAAMI pressure limits increase, the best propellant will typically exhibit a relatively slower burn rate.
So much for facts and theory. Let's get practical.
Hodgdon surplus 4831 cost about a dollar a pound when I first began reloading about 38 years ago. H4831 is listed at the slow end of the burn-rate chart. It's most suited for full-case charges in the .270 Win., 7mm Rem. Mag., .30-06, or .300 Win. Mag. with medium- to heavy-weight bullets. But will it perform safely and reliably in smaller- capacity cartridges, such as the .308 Win., 7mm Mauser, or .244 Rem. cartridges?
The answer is a qualified, "Maybe." So will most small-arms propellants--some better than others, of course. It all depends on what your success criteria are. If each bullet always strikes the target exactly in the same place, the benchrest competitor will be ecstatic. If the same load/firearm is used for hunting or law enforcement and the game or bad guy is not immediately incapacitated, then the responsible sportsman or police officer will definitely not be happy.
Ideally, you want to achieve maximum loading density with a propellant that launches the bullet to the highest velocity without exceeding the industry-specified maximum average pressure (MAP) and also delivers the desired accuracy. Loads that almost fill or even slightly overfill the case (i.e., typically not more than 5 percent compression) and achieve near maximum MAP are considered to be the most efficient. That's from an internal ballistics perspective, of course.
If a specific combination of components doesn't produce the external and/or terminal ballistics performance you desire, then it's practically worthless. That's when reviewing and comparing the various burn-rate charts can fit into the overall scheme of handloading.
Let's say you tried a specific powder, primer, case, and bullet combination, but it just didn't deliver the accuracy, velocity, etc., you want. The burn-rate charts will indicate other candidate propellants that are ranked close to the one you've already tried, and one of them may achieve satisfactory performance. However, you still must research other sources to determine safe reloading recipes using the alternate powders.
A stern word of caution: Never use a burn-rate chart to select another propellant and then simply duplicate the charge weights of one you've already tried.
If you unilaterally plug and play a substitute powder, you can damage the firearm, and you may be seriously injured or killed. Practically speaking, burn-rate charts are only comparative guides to help you develop alternative handloads while searching for the right load that delivers the best performance in your gun.
Relative Burn Rate Listed From Fastest to Slowest
