Rifles and rifling

by Fred Ray on May 6, 2008 · 3 comments

The 19th Century saw the most rapid improvement in the rifle of any comparable period in history. At the beginning of the century the exemplar of the standard arm was the smooth bore .75 cal. Brown Bess musket, and by the end we have the modern .30 cal. bolt action, box magazine repeater using smokeless powder (not to mention the Maxim gun).

The Brown Bess had the longest service life of any service arm. The design went back to the 1720s and it served in the Seven Years War, the American Revolution, and the Napoleonic wars. Even then, the Duke of Wellington was loth to give it up for the rifle musket. Converted to percussion, some remained in service in parts of the Empire until the late 1850s.

Eventually the British Army did get around to adopting the rifle, but there was a great deal of variation in the types of rifling and intense debate on which was best. The Volunteers, a sort of self-armed, self organized militia, were a great laboratory for this, since they (at least until 1862) furnished their own weapons and also shot a great deal in long range target matches. You can click on the image for a closer look, but the first two are standard 3 and 5 groove barrels. The third is the oval bore Lancaster that I mentioned earlier. The last is also interesting, as it is similar to the Whitworth and modern “polygonal” rifling designs.

Almost all these designs used a soft lead bullet of .57-.58 caliber and very deep grooves. At the moment of firing the bullet “upset” and had its skirt forced into the grooves, which made it spin. This did cause quite a bit of friction, however, which slowed the bullet down considerably. It surprised me to learn that the initial velocity of the smooth bore musket was considerably higher than that of the rifle, 13-1500 fps as opposed to 850-900 for the rifle. Of course the round ball of the smooth bore slowed down much faster than the cylindrical bullet of the rifle musket, but over short distances it did have a a flatter trajectory. The rifle, OTOH, had a looping “rainbow” trajectory that made long distance shooting difficult. Get the range wrong and the bullet would pass considerably over your target’s head or hit well in front of him. Thus the core of most mid-century marksmanship programs was distance estimation, since it was impossible to hit anything accurately without knowing it.

Here’s an illustration of the problem—a .45-70 black powder round compared to a modern .308/7.62 NATO round. Note that it’s not really a “rainbow” trajectory. The round drops sharply at the end of its ride as its energy falls off and air resistance increases.

In the next few nights I hope to review Joe Bilby’s new book on the small arms of Gettysburg and further explore some of these topics.


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{ 3 comments… read them below or add one }

Drew W. May 6, 2008 at 11:27 pm

Fred,
Coincidentally, I just started the Bilby book today.

The whole comparative muzzle velocity data seems all over the place, and I must admit to not having seen quite the degree of disparity you mention, which is massive. Although current writers mention the higher muzzle velocity of the smoothbore musket, I recall coming across a chart from a firing test that determined that the rifled musket had a higher muzzle velocity than a smoothbore (but by a very slight margin…10-20 fps or something like that). I wish I could remember the source.

I suppose you could look at the matter in different ways — the rifle has more friction from the engagement of the skirt into the rifling grooves, but it also has the propellant gases “sealed” behind it; as opposed to the round musket ball which is loosely bouncing along the inside of the barrel.

I am looking forward to Earl Hess’s book about the rifled musket, to be published by UNC later in the year.

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Fred Ray May 7, 2008 at 7:08 am

Surprised me too. The info comes from 19th C texts but has been confirmed by modern chronographs. Apparently the soft ball “upsets” when fired and does a better job of sealing than thought. Bilby goes into this in some detail.

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Craig May 7, 2008 at 8:26 am

Personally I’m a bit more familiar with the rifling techniques used on the cannon of the ACW period. But the base technology is the same. One difference I’d point out, rifled muskets did not have, or don’t seem to have had, as many issues with bore pressure as the rifled cannon. Hexagonal rifling, as seen with the British Whitworth cannon, just didn’t play out well. The corners formed within the bore created stress points, weakening the overall gun.

Also of note, Parrott rifles employed a gain-twist rifling, increasing in pitch from the seat to the bore. Hard to really gauge now days (what with pigeons nesting in the bore). I’d be interested if any of Parrott’s notes regarding the choice of this technique exist.

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