Muskets, rifles, and rifling

I found several emails from Bill Adams, who is kind enough to provide me with a lot of information about black powder period arms. As for the higher muzzle velocity for the smoothbore musket, he points out three factors:

1. Many musket cartridges came with a paper patch, which helped sealing somewhat
2. The round ball upset when fired, elongating to fill the bore to some extent. This did bad things for accuracy, however.
3. The blow-by reduced recoil, allowing more powder for weight of ball. This had to be reduced considerably for the Minie rifles to keep recoil bearable.

Bill adds:

While these figures are rounded off, consider that a 100 grain charge behind a 474 grain .680″ round musket ball gives 4.74 grains of bullet weight for every grain of powder. 60 grains of powder behind a .575″ 500 grain rifle bullet gives 8.3 grs of bullet weight for each grain of powder. The musket has nearly twice the propellant to bullet ratio as does the rifle. Now, if we increase the rifle charge to 100 grs and use a .575 ball at apr 272 grs, we would have 2.72 grs of bullet for each grain of powder, and bump the velocity way up. Shoveling a 750 gr hollow based bullet into a rifled .69 smoothbore and having to drop the charge to 80 grs to curtail severe recoil, gives us 9.38 grs of bullet weight for each gr of powder & the velocity will drop to possibly half that of the smoothbore with a round ball. The trajectory will increase, but so will the effective range.

Different rifling systems caused more or less drag, depending, and this seems to have been one reason for the progressive depth grooves (i.e. shallower toward the muzzle) on some rifles. Bill also suggests tha some muzzle loaders may have had m.v.’s of close to 2000 fps. Tolerances of CW-era guns were often quite loose, both for barrel diameter and ammunition sizing, because the soft lead bullets could compensate for a lot of variation.

The only man to get around this conundrum was Joseph Whitworth. I have mentioned Sir Joe’s rifles in a previous post that I see Brett has reposted on this blog. Sir Joe used a mechanically-fitted bullet, that is the hexagonal bullet fit tightly in the hexagonal bore, closely enough to prevent blow-by. Thus, with the same powder charge, he got all the benefits of rifling with the velocity of a smoothbore. The only drawback was that the tight tolerances were expensive to manufacture and more prone to fouling. Since it did not have to expand to grab the rifling, Whitworth could use a hard bullet rather a soft lead one, which gave better long range performance.

Nevertheless, this was not the last word on the subject. Two other Brits, Metford and Halford, were exploring the same terrain. They concluded that it was feasible to use a hard alloy bullet with extremely shallow grooves, providing the sizing was consistent and the bullet had a hollow in the base. This reduced drag and allowed the bullet to travel as fast as the Whitworth.

Bill says: “Halford showed up at a 1000 and 1100 yard match at the Cambridge University Long Range Club in June 1865 with a Metford rifle with five .004″ deep grooves and was ridiculed by everyone there as having a ‘smoothbore.’ Halford won the two-day match, being four points ahead of the nearest competitor.” Compare this with the Enfield grooves which were .013″ deep. It proved to be the wave of the future, and the Whitworth gradually lost ground to the new rifling systems of Metford and Henry (not the US repeater), and had been pretty much supplanted by the 1870s. Compared to the Whitworth, the new rifling systems were easier and cheaper to manufacture and less prone to stripping or fouling. With the adoption of the breech-loader and better manufacturing facilities, the hard bullet/shallow groove combination became universal, as it pretty much is today. Around the turn of the century armies adopted smokeless powder, which bumped m.v.’s to 25-2800 fps, and the pointed “spitzer” bullet to make the modern rifle as we know it today.

UPDATE: If you’d like to learn more about William Ellis Metford and his rifles, read this article in the 1901 Dictionary of National Biography. The adoption of the hard alloy bullet did have one interesting corollary—a reduction in stopping power. The previous soft lead bullets (such as those used in the ACW) tended to expand when they hit, transferring a lot of energy to the target. The alloy bullets didn’t, leading to the introduction of the “Dum Dum” bullet, subsequently banned. For a much longer contemporary (1902) look at the Lee-Metford rifle, bullets and their effectiveness, see this article in Blackwood’s.

UPDATE 2: I should have mentioned that the Whitworth used two types of bullet. The “standard” hard alloy hexagonal bullet and a soft lead cylindrical bullet. Each rifle (at least the ones used here) came with a bullet mold that cast a round bullet, this in case the factory swaged ones were not available. When fired, the round bullet “upset” to the form of the bore, becoming a hex. It had different flight characteristics and the sight was marked “H” on one side and “C” on the other so the rifleman could adjust correctly. Relic hunters tell me that the cylindrical rounds are far more common.

The Euroarms site has photos of Whitworth and Henry replica rifles. The Henry (no relation to the American repeater) used rifling designed by Alexander Henry and managed to equal the performance of the Whitworth with a conventional design. These were highly regarded match rifles and some may have been used over here.

UPDATE 3: A very good primer on ballistics “for dummies” in Rifle Shooter magazine. All the basics plus arcane terms like sectional density and ballistic coefficient, written in a readable manner.