Dominick
The breechloader was designed by Martin von Wahrendorff in Sweden and made at the Aker foundry in 1846. Here's a picture of how it works from Holley's book of 1866. As you say, it is remarkably similar to William Armstrong's much later breech loader, even down to the lead-coated projectiles. The Wahrendorff gun was different in being of the finest Swedish cast-iron and not built up from Armstrong's wrought-iron hoops.
Starr