As a long time student and enthusiast of John Dahlgren
I collect Dahlgren stuff too, I also have found some manuscript items by him and some mentioning him, that I hope to publish some day. I collect the Dahlgren-associated gunnery items too, his gun firing locks, models, cannons when I can find them, etc.
I still need a "small" Dahlgren boat howitzer on original carriage, just missed one a few years ago. I was looking for the rest of the money, trying to sell my cat, my wife, etc. when somebody who had the money showed up and bought it. They made 23 of them, and I think two are privately owned. I need that one to complete the trio of the models that could be mounted on field (landing) carriages, so if you see one of the small 300 lb. tube specimens for sale, pls let me know.