According to the ex commie who lives in the neighborhood behind me, and grew up in Russia, it’s pronounced Moe-seen Nahgahn
The T is silent in Nagant.
That's how Hickok pronounces it initially and is probably correct. Then for the rest of the video he pronounces it phonetically as MOE-sin Na-GAHNT, which I'm guessing is the most common way you'll hear it.
If that’s the case then Nagant must be a borrowed name because there’s no such thing as a silent T in Russian.