Hi Norman
Something else you may have to consider if your sword was sold on your side of the pond would be; "What is an American sword of that period doing abroad?" One chapter of Mowbray's eagle book begins with an example of a sword specifically made for a Scotsman. Perhaps you can fill in some blanks yourself on how you came to own the sword and where it had come from.
In America, other warring aside from the war of 1812 and up to the American Civil war would be notably the Seminole wars and the Mexican War. Throughout the interbellum periods were standing militia, as was also true in the UK.
Swords were made up of many standard parts, some fancier than others. Often times there would have been a basic catalog of options, as well as "floor models" to choose from. I have already alluded to that the large head floating pommels are less common post 1812 but showed you an example while mentioning I have more in my own bank of images. You now bring up the spiral grip as uncommon and I agree but could list a few in my own files. MOst of this general time period and in a romp through one of my misc folders have a good match to your own sword. What does that mean in terms of scarcity? Not much. When you find a couple, chances are that if persistent they seem to come out of the woodwork.
I mention in another post that eagles are a passion. That I have some 6,300 eagle sword image files in 41 folders must mean something. Divide roughly by whatever and that would still be many more than six hundred swords I am in the process of categorizing. Consider my prime focus of the eagle pommels to be those up to the war of 1812 and of three basic forms (Bolton, Osborn, Ketland), I will never have half the answers to a good many questions. Narrowing to a couple of decades should be an achievement and as you had already considered the 1830s, I think you may not have just been guessing.
The langets might also point to Solingen as opposed to England but again, the blade decoration too Birmingham blue&gilt to disregard. The example I showed above has noo langets and a good many British made swords for the American market had no langets. That trait also prevelant in American manufacture. On that note, I seriously doubt it is American cutlered and eveb the Spies marked blades decorated and marked at that time in England, as that is how they were ordered.
Along with your spiral big head, I'll also scare up an British made Ames imitator with a spiral grip. So close an imitator of the Ames swords that I was fooled in the beginning myself. That conflict worth a whole thread by itself someday but brought up here in the past. Why do I know that one British and not American Ames? More study and observation to be related someday.
This one most assuredly the mid to late 1830s.
Oh, ok, I lied. Here is one I am pretty sure was an Ames eagle casting but on a Mexican sword (Ames did collaborate with Mexico before the war.
Cheers
GC