Is this a thread about Andrew's 38/640 or Andrew_ASC's life story about his experience?
Andrew, it appears you have an AMW case. Unfortunately I think that AMW stopped making loads when Paul passed away. AMW's site does not show any 38mm loads in stock.
I think you may have experienced a moment of "buyers impulse"... And now you may learn a new lesson, if you so choose to learn it -- you'll experience it anyway... Buyer's remorse. You need to understand what you are buying BEFORE you buy it. 38/640 as you learned applies to two different manufacturers, and that's a tough break.
While it is nice to see the unbridled enthusiasm, we also wish to help you learn these lessons early on. I'm a terrible teacher about life lessons because, well, I went through all this and probably didn't learn what I needed to learn (then) until much later in life.
Hopefully you find good purpose for this casing. Maybe you can reach out to Scott Kormeier at Loki Research to see if his loads are compatible with the casing that you have.
Hope you are able to use your new acquisition in one way or another.