In the records of the United States Congress there is a document entitled Proceedings And Recommendations Of The Board On Heavy Rifled Ordnance, Instituted Under the Act of June 6, 1872, For The Selection Of Breech-Loading and Muzzle-Loading Rifled Ordnance For Experiments and Tests. The Board on Ordnance met in the summer of 1872 in New York City and it appears that one of the things they were doing was attempting to select a new type of artillary gun for the army. Merritt Griswold is mention in the minutes from the board's August 14, 1872 meeting.
New York, August 14, 1872
The board met, pursuant to adjournment, at 10.30 a.m., all members being present.
A letter from the Chief of Ordinance was read, transmitting the report on an 8-inch gun of Mann's pattern.
The board then proceeded to a consideration of the propositions of Nathan Thompson...of Brooklyn, New York, and, after discussion, they were laid over for the present.
A letter was received from Merritt W. Griswold, of New York, calling attention to the breech-loading and breech-recoiling gun inventedby Mr. Henson. The letter was accompanied by a drawing. Mr. Griswold was present, was invited to meet the board on Monday next.
The board then discussed the feasibility of a plan of converting cast-iron smooth-bores into rifles. No conclusion being reached, the board adjourned to 11 a.m. of the 15th instant.
Griswold is mentioned again in the minutes from the board's meeting on August 19th:
August 19, 1872
Messrs. Merritt Griswold and Henson, being present, exhibited a model of the Henson gun, and described its mode of performance and its construction. After the withdrawal of these gentlemen, the gun was discussed and the following resolution was passed unanimously:
Resolved, That the board does not recommend for experiments and tests,under the provisions of the act of June 6, 1872, Henson's breech-loading and breech-recoiling gun, presented by Merritt W. Griswold.
In the appendix of the Board's report, two letters that Griswold wrote to the Board are reproduced, along with the drawings of the Henson Gun submitted by Griswold:
Office of Merritt W. Griswold & Co.,
104 Chambers street, New York, August 14, 1872
I beg leave to submit herewith a drawing (a gun will be also submitted if desired) of "Henson's breech loading and breech-recoiling gun,"that in actual practice has given results superior to a solid gun of the same caliber, and accomplishing much beyond the impressions formed by a theoretical examination.
At each discharge the butt recoils from the barrel proper, which latter does not appear to receive the least shock, thereby leaving a clear open space for reloading.
A trial was made of placing an independent paper wad between the powder and breech, and it was left in the same position after the discharge that it occupied prefiously, though the shot had been projected with great force and the breech recoiled to its proper position for reloading.
Hoping to hear from you, I remain yours, &c.,
Merritt W. Griswold
The second letter gives more details about the specifications of the Henson gun.
I think several things can be learned from this information. First, this is more confirmation that Griswold was a mechanical engineer. Second, he was living in New York in 1872. This is important because it's difficult to track Griswold's movements in the 1870's and 1880's. Finally, this gives us the name and address of Griswold's company-Merritt W. Griswold & Co. on Chambers St. in New York.