A Bore-ing Day at Manassas

Yesterday the staff and I took an afternoon trip to Manassas to burn off what energy we had left after a day of yard-work.  While on the Henry Hill trail, I took the opportunity to take “measure” of some familiar guns.

Manassas 25 June 11 064
Bore of 6-pdr Model 1841, Alger #111

I’ve always carried a tape measure and small ruler with my camera/field bag.  But until recently I never had a camera that would provide the close-focus resolution to make pictures worth posting.   The subject of this photo is a 6-pdr Field Gun produced by Cyrus Alger in 1854.

According to the 1862 Ordnance Manual, the 6-pdr’s bore measured 3.76 inches (that is 3.67 inches for the projectile plus 0.09 inches for windage).  In the photo my ruler stands at a slant, but I’d call the measure about 3 and 50/64ths, or 3.78 inches.  Considering this gun is over 150 years old, been in the elements for much of that time, and has scars to attest to heavy use – that’s not bad.

Moving down the line, another 6-pdr, this one produced by Miles Greenwood’s Eagle Foundry in Cincinnati, Ohio, in 1861, has similar measures.

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Bore of 6-pdr Model 1841, Greenwood #11

Again, adjusting for the placement of the ruler, I’d call it 3 and 50/64ths.  Not as much scarring in the bore of this “western” gun, however.

On the other hand, the bore of a Model 1835 6-pdr now measures a bit more.

Manassas 25 June 11 028
Bore of 6-pdr Model 1835, Ames #11

This is Ames registry #11, cast in 1837.  It’s bore measures about 3 and 54/64ths in diameter.   Maybe it was fired more?  Maybe the inspector allowed a bit more windage?

Now how about the rifled field guns?

Let’s start with a gun that started life as a smoothbore.

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Bore of Rifled 6-pdr, Ames #176

Ames produced registry number 176 as a smoothbore in 1854.  Either just before, or in the early stages of the war, the gun was rifled.  The bore went from 3.76-inches to what I measure at 3.84 inches (3 and 56/64ths to keep on the same scale as the smoothbores noted above).  Note the rifling lands on the upper bore barely touch the “28” and “56” marks on the ruler.

Another gun on the line shares the same Model 1841 pattern, but was ordered from the start as a rifled gun.

Manassas 25 June 11 054
Bore of Ames #530, James Rifle Type 1

Ames Manufacturing produced registry number 530 against an order for 6-pdr rifled guns.  I’d measure this bore with a bit less windage at 3 and 13/16ths, or 3.82 inches.   Bore wear?  Or increased tolerance on guns produced as rifles from the start?  My field notes over the years lead me to believe this is a case of wear.

But compare to the wider bore of the 12-pdr field howitzers on the same line.

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Bore of 12-pdr Model 1841, Marshall #23

By the manual, the bore should measure 4.72 inches.  In this case, the ruler measures to the 46 mark past four inches, for 46/64ths.  That’s very, very close to the regulation measure.

I made some interesting measures of the Parrott rifles on the Federal side of the line, but I’ll save those for a post comparing Tredegar and West Point Parrott rifles.

Hundredths of an inch.  But every hundredth important to the weapons performance.

4 thoughts on “A Bore-ing Day at Manassas

  1. I suspect you are confusing production tolerance limits with windage. Windage is the bore minus the projectile diameter. It is not intentional oversizing of the bore. The dimensions given in the manuals and on drawings are the correct nominal ones. They would not be oversized by adding windage. Instead projectiles were slightly undersized to provide windage.

    The bore size is a nominal size. One would expect that to pass inspection with the cylinder gauge, and allowing for machining tolerances, the bore would typically be a little greater than nominal.

    • Actually, no this is what the manual refers to as “true windage”. The bore size is indeed, as you point out, measured by a cylinder gauge. But as anyone who has worked with machine parts can attest, such a gauge would become unwieldy in a cannon bore. So even the gauge had to have “windage.” This became the deviation allowed in the bore. For field pieces, this would be around 1/100th of an inch or less.

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