Kerry-
That particular helm was three piece welded construction for the skull (the two halves in 12ga CRS and the aventail in 14ga CRS), the visor, cusp plate and bevor were all single piece 16ga CRS. I have hot raised helms and smaller kit in one piece, like this umbo (center hand protection for a shield);
but that takes a lot more time and resources than most people are willing to pay for.
Here is a little repousse on the top of a topfhelm in 13ga CRS.
And here is how it looks on the inside;
I am an engineer by trade, worked my way up from the fabrication side, and it always gives me a smile to realize how my metal working hobby influences how I design equipment in my day job!
I just began to peruse the site, a lot of serious talent here!
Cheers, Erick