Ed Yard, a well-known ballistician, noted these differences and disagreed with such black powder wisdom as not being able to load black powder in a modern firearm to produce excessive pressures. Thompson/Center Arms sponsored Yard to conduct accurate pressure and velocity tests in rifle barrels.
Using the crusher method with lead crushers rather than the standard copper of the CUP methods, a series of tests was begun. Pressure figures are, accordingly, listed herein as LUP and CUP -- not to be confused with psi (pounds/square inch) which is an entirely different unit of measure. Yard's work is published in Guns Magazine and Muzzle Blasts, journal of the National Muzzle Loading Rifle Association. Lyman Products for Shooters also conducted extensive pressure and velocity tests with various powders for its “Black Powder Handbook.”
Yard estimated performance variations of 15 to 25% among the various powders available at one time or another in the USA, but since samples of all the old powders weren’t available, these estimates reflect variations in more modern powders. Early variations in powder performance derived from such factors as component quality, grain size, mixture proportions, moisture content, and from the fact that early black powder was a mechanical mixture of the components salt peter (potassium nitrate), sulphur, and charcoal. Modern black powders are "corned" wherein the mixture is wetted and ground into a homogenous slurry then dried and broken into grannules. Mechanical mixtures of black powder often separated while aboard rocking ships, bouncing wagons, and in the powderhorns of hunters and soldiers. Keeping black powder in a uniform mixture through stirring, turning, shaking, and the like was an important aspect of ensuring consistant performance in the charge.
Yard discovered that in round-ball rifles, a charge weight greater than ball weight produced increase pressure with little increase in velocity. When charge weight exceeds ball weight, efficiency drops drastically. Ash fouling from black powder constitutes about 57 percent of its original weight. As the amount of this residue increases, the force required to drive it out of the bore rises exponentially.
In specific tests of a .50 cal. Hawken barrel, Yard established that increasing the powder charge beyond 170 grains actually reduced muzzle velocity. The same result was obtained in .45 cal. at the 130-grain level, which represents approximately equal weights of powder and ball.
Historically, shooters didn’t know this.They reasoned that if some powder was good, more must be better. Large charges weren’t especially common in the East with Kentucky rifles, but out West a .50 or .58 cal. Hawken might be loaded with as much as 200 to 250 grains of powder. Mountain men knew that a good rifle could withstand such charges without damage. The larger smoke cloud, brighter muzzle flash, and greater recoil were all the proof they needed that the rifle so charged “shot harder.” In actuality, the greater recoil resulted from the energy required to push ash out of the barrel and was entirely lost on the bullet.
Kentucky rifles were sometimes fired over fresh snow with successively larger powder charges until unburned powder granules could be found on the snow. The greatest amount of powder that could be loaded without showing unburned grains in the snow was considered the maximum usable charge although not necessarily the most desirable charge. Yard never tested the accuracy of this system.
Yard checked properly patched balls against the same ball used naked, as in the hurried loading of battle. When a loose ball was rolled down the bore against the powder, velocity was about 25O fps less than when patched--this on account of back pressure being essential to efficient combustion of black powder.
Velocity gain per inch of barrel beyond 28 inches is approximately 8 fps per inch, declining gradually until at about 42 inches there is no velocity gain from increased barrel length. Velocity may be expected to drop as bore friction negates the velocity gains of an increased charge
Other factors being equal, that the heavier powder charges generally used in the West more than compensated for the theoretcial gains of the longer barreled Kentucky style rifle.
Overcharging the BP rifle--
The claim that black powder firearms cannot be overcharged apparently derives from the use of metallic cartridge loads or revolver loads where the mechanical limits of a maximum charge fitting the case or cylinder would not produce excessive pressure. Yard found that indeed a muzzle loader can be overcharged. We should note here that modern smokless rifles are engineer to function in the realm of 50,000 CUP or more, while the muzzle loader is designed for about 10,000 CUP. Smokeless powder develops an entirely different pressure "spike" and has altogether different combustion features than black powder.
45 caliber loads range from 70 to 100 grains, and this load range produces (with FFg ) approx. 4400 to 7500 LUP. In .50 caliber, 80 to130 grains charges in ten-grain increments produce pressures of 4300, 4600, 4700, 5000 and 6000 LUP. The ten-grain increment from 120 to 130 grains increases pressure a full 1000 LUP, more than three times the increase brought about by 10 grains at any lower level. In heavy loads, increased charges elevate pressures exponentially rather than in a straight line.
A fouled bore will increase pressure, as will greater patch thickness or greater ball diameter. Tests with the SAME patch showed shortening lubrication increasing pressure by 1500 LUP over one lubricated with spit.
Patch thicknesses of .011 inch, .016 inch, .018 inch and .021 inch yields 3600, 3700, 4300 and 6000 LUP, respectively. Note that pressure increases 1200 LUP with the increment of .003 inch from .018 to .021 -- 17 times more than the proportionately larger step up from .011 to .016 inch, and nearly three times the increase from .016 to .018 inch.
The effect of these variables on working barrel pressures can be cumulative or exponetial depending upon their configuration. In some instances greater working pressure does NOT yield higher velocities. A tight patch in a fouled bore may overstress the barrel with little increase in velocity. OR, variations may tend to cancel out each other -- a strong argument for consistent loading protocol and for changing only one variable at a time when working up a load.
In attempting to increase muzzle energy of the muzzle loader, some shooters have opted for "double ball" or "buck and ball" loads--the latter being a load of buckshot over a round ball. In .36 caliber, Yard found a single-ball load produced 6300 LUP, while two balls produced 12,300 LUP. A .45 cal. single ball yielded 6400 LUP, double ball 12,600 LUP. One might expect heavier elongated bullets might also overstress the gun highly. Though such bullets generally weigh about twice as much as a round ball projectile, pressures do not increase as with the double ball loads. 45 cal., 230-grain Maxi-Ball charged at100 grains showed 7000 CUP, compared to 3600 CUP for the round ball. In .50 caliber the Maxi-Ball charged with 100 grains produced 7300 CUP, compared to 4200 CUP, or the round ball with an identical charge. In both calibers the twice-as-heavy Maxi-Ball achieved a velocity roughly 80-85% of the round ball.
Elongated bullets make much more efficient use of powder. In .45 caliber the elongated bullet produced 11 fp of energy per grain of powder, while the patched ball produced only 8.6 fp per grain--a 28% advantage.
With a standing charge of160 grains FFFg and uniformly patched balls, a 30-inch barrel yielded 1972 fps; a 34-inch 1973 fps, and 43-inch 2113 fps.- a 140 fps increase for 13 inches increased barrel length or 10.77 fps per inch. In a 28-inch .50 caliber barrel pressure increases with little gain in velocity when loading powder charges in excess of ball weight.
In loads ranging from 50 to 200 grains FFFg in 10-grain increments and 180 grain round ball: 50 to 60 grain increased velocity 100 fps, 100 to 110 grains the increase diminished to 41 fps, 150 to 160 grain only 12 fps, 190 to 200 grain drops to 10 fps increase yielding a velocity of 2071 fps. Pressure increased in the realm of 150 to 450 LUP per 10-grain powder increase in the mid range of loads, but the final 200-grain load, produced nearly 1000 LUP increase. In the mid range loads, velocity gained at about 1 fps per 7 to 9 LUP. The maximum charges gained only 1 fps at pressure increases of 90-100 LUP. In heavy loads, the last few fps are gained at very high pressure increases and increasingly inefficient powder consumption.
It's important to realize that various brands of black powder produce variable pressure/velocity statistics, but the characteristics of pressure/velocity yields for similar loads are consistant from powder to powder. The principal variable in black powder performance is produced through grain size with finer grain powder producing faster burn rates and higher working pressures.
Even after smokeless propellants came into general use, there continued to be a need for the unique characteristics of black powder. The combustion rate of nitrocellulose or nitrocellulose-nitroglycerin, smokeless propellants increases as chamber pressure increases. Black powder shares this characteristic somewhat but as applied to muzzle-loading guns, however this combustion acceleration is not significant. If an overcharge of black powder is used, pressure will rise proportionately until the excess powder blows out of the barrel--20,000 psi even with an overload. Working pressures with smokeless powders in modern rifles are 50,000 psi or greater, and as little as 10 percent increase in the charge may dangerously increase pressures.
While Pyrodex does produce fouling similar to black powder, there is much less of it, and it interferes less with loading. In tests, patched-ball rifles have been, loaded and fired with Pyrodex as many as 100 consecutive shots without cleaning, yet ramming effort remained normal. This is not possible with black powder.
Pyrodex fouling seems to have a self-lubricating quality, and best accuracy is obtained in some rifles without lubricant on either patched balls or bullets (which of course affects working pressures as compared to lubricated patches/bullets). Pyrodex fouling, moreover, produces an advantage in ballistic consistency. Consecutive shots using black powder without cleaning will yield significant and erractic shot-to-shot increases in pressure and velocity, and a decrease in accuracy.
In strings of 50 shots or more, Pyrodex pressure and velocity values remain constant. Pyrodex produces ballistic consistency without cleaning superior to the ballistic consistency obtained with black powder by thorough cleaning after every shot. With either propellant, residue left by the initial "fouling" shot increases pressure and velocity on the second shot with this increase being about the same for both propellants. After the initial fouling shot, however, Pyrodex remains consistent in pressure/velocity without cleaning the bore, while black powder produces increasingly erratic performance.
Pyrodex contains corrosive salts similar to black powder, but also contains a rust inhibitor. Pyrodex fouling is hygroscopic and cleaning is mandatory after use, but there is a little more margin for forgetfulness. While either propellant will rust a bore that is left uncleaned, Pyrodex is somewhat slower to rust the steel.
No propellant ignites as easily as black powder. Hangfires and erratic ignition in side-lock rifles are more common with Pyrodex than with black powder. Most Pyrodex ignition problems are solved by switching to hotter caps, and/or by thoroughly cleaning the ignition path. Firing a cap into an empty chamber rids the ignition path and bore of residual lubricants and is a good practice for either propellant. .
Most caplock revolvers experience no ignition difficulties when the ball is firmly seated against the charge. Seating reduced loads in revolvers requires that the ram lever be of sufficient length to seat the ball firmly in the cylinder against the powder charge.
The above characteristics notwithstanding, tests have shown no significant difference between the performance of Pyrodex and the related grades of black powder when used according to recommended guidelines. Accordingly, all precautions applying to black powder apply to Pyrodex as well.