The effective range at various elevations and charges

*does* end up published, which is because it provides the basis for those calculations to be done. Artillerist's manuals also included rules of thumb, such as the British artillerist's manual of 1860 laying out a rule of thumb which was:

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Obviously this

*is* only a rule of thumb, but it provides a starting basis. For a 12 pounder firing solid shot at 900 yards the gunner could say that it is 260+640 yards, and thus that he should start with the gun pointed directly at the target and then elevate by 1 1/2 degrees.

For shell, meanwhile, a table such as this would be consulted:

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And at 900 yards then by interpolation it would be a little over 1.5 degrees and expected to have a time of flight of about 2.6 to 2.7 seconds, with a deflection allowance of 6-7 minutes right.

Or this table could be consulted:

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Which shows that at 900 yards it would be 1 degree 32 minutes of elevation, and a deflection of 8 minutes right.

These calculated figures form a basis for the gunner to adjust from.

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As noted, the deflection is not significant at short range for the Armstrong gun (i.e. below 2000 yards). This makes sense because at 2000 yards the size of the 360 degree circle is 12,566 yards; this means 1 degree is 35 yards and one arc minute is about half a yard. So a deflection at 1000 yards of 8 arcminutes is about 2 yards, thus why the book describes it as negligible.

Similar tables for the Parrott, Ordnance or Napoleon would, of course, be fascinating.