According to King and Wilson, p. 307, Kudin opened fire about the same time Yurovsky did. Both fired at Nicholas II.
So, this eliminates Kudrin's Browning.
So, we're back to Ermarkov. Two of his four guns were a Mauser and a Nagnant.
King and Wilson wrote on p. 302:
>>Ermakov had come with two Russian Nagants. Yurovsky handed him a Mauser and a Nagant[/red].+ Dangerously weighted down with four revolvers, Ermakov's belt saged, the sight, as Kudin recalled, so absurd that "we all had to smile at his armed appearance." <<
So, if the bullets didn't come from the Brownings of Kudin and Nuklin, and, Ermakov did not have a Browning, then who did?
AGRBear
+ A line I somehow missed when I was typing out this section in my earlier quote.