Not sure why it didn't load for you. I can see the videos above.
Go to this old thread titled "FN PS90?" and look at post #32.
https://www.mdshooters.com/threads/fn-ps90.188641/
Here is a picture of my favorite AR57 set up. I have one of these, but I had a custom suppressor built about 3" longer than the one in this picture. This is a hard round to suppress so I went with more length and a few more baffles.
That is an AR57 upper with 12" barrel. It is on a full auto registered receiver with full auto bolt. It uses FN P90 50 round mags and ejects the rounds down through the mag well. Very fun, and controllable gun to shoot.
That is the Hammer Letter Series USA H-D model with 4.5" barrel. They also came with a 6.75" barrel. 34,000 produced. I thought that they were only produced in 1943, but that may not be correct. Those are the correct hard rubber grips for that gun.
That is the base gun for the USA H-D MS...
Nice find J!!! They are rare. I've got an H-A with 4.5" barrel and one with a 6.75" barrel. The HE was not actually the least produced. That was the Hammer Series H-D. (Aside from the model S with 14 total) John Simson told me many years ago that actual production count for the H-D was...