Here’s a photo of three of the .400 Whelen that you asked about on another thread. If I remember correctly, these belong to Pete deCoux. Mine are very similar, with an FA 22 R headstamp, and with no headstamp.
There are actually 2 versions of the 400 Whelen. The original that was made from a cylindrical case necked down to 40 caliber, and those that were made from 30-06 brass necked up to 40 caliber. The difference between them being the shoulder diameter. Of course, if you take one of the latter and fire it in an original chamber, it will expand and come out looking just like an original. But you cannot do vice-versa.
Now that I recall, the empty case on the right may be one of the latter versions. Pete might remember. I don’t. And the one you showed in your thread may be one of the later ones also.
Did you have a chance to measure your 46 American? I’d still like to get the case length and bullet diameter.