Here's a portion of the Lt. Bell's report of the second series of tests of three different types of 6-pounder guns. I've annotated it by adding a line for the SNY-marked cannon so you can see how some of its measurements compare with the "Brass gun" that Bell tested. As you can see the measurements I took of my gun (in blue) match fairly closely the "Brass gun" fired by Lt. Bell. The 10-lb. weight difference would probably have been within the tolerance for weight variation of the model, since the two measurements differ by only 1.5 percent.
The gun length measurement is the only significant difference between my gun and the two brass guns tested by Bell (at least as far as I can tell from the data he recorded.) I'm assuming Bell used the "nominal length" measurement which is taken from the muzzle face to the rear of the basering, and this measurement on mine falls noticeably short of Bell's test gun. I suppose that accounts for the 10 pounds by which Bell's gun outweighs mine.
I can't explain the length difference, which would normally be too much for an approved model where the government gives the contractor the drawings and says in the contract to build it to those drawings. Perhaps with this undesignated model of the "brass gun," each of two or more founders built their own patterns, flasks, etc. based on looser guidance from the government.
Or, since there are thought to have been "a few" contracts for these brass guns, there could have been a change in the model that was directed by the government, in the interval between two of contracts, and my gun was delivered under a different contract from the one that produced Lt. Bell's two brass guns.
I'll put the links in below so you can see some of the other parts of the two reports.
Lt. Bell conducted his extansive firing tests with one group of three guns in September 1827. The powder charge for all shots was 1.5 lbs.
Then he got three new guns of the same types as in the first series of tests, and repeated the tests, with a smaller powder charge (1.25 lbs.) This series is covered in the November report.
His goal in both series was apparently to fire 2000 rounds through each gun, or until a gun became unserviceable. He fired all three guns simultaneously using three lanyards that were pulled as one, and kept up the amazing rate of fire of about one round per gun per minute while firing.
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