Many of the contracts for the Allies that were placed with companies in the United States were placed by the British government through their agents J.P.Morgan.
This was partly because Britain had the infrastructure in place with British or Canadian inspectors in the factories and Morgans looking after contractual arrangements, and partly because Britain was guaranteeing payment.
Probably the best known examples are the Russian contracts for the Mosin nagants, with Winchester for Model 95 muskets and with Colt for Government Model .45 pistols (which even had “English Order” stamped on the slide in Cyrillic).
I will have to check the contract details, but I think the Hopkins and Allen contract for Belgian Mausers was placed directly by the Belgian Government and so probably was the ammunition order with Remington. In the UK, Greener was making Belgian Mausers at the Bagot Street works in Birmingham and Nobel was making ammunition for them.
The research and study of these contracts, both for small arms and ammunition is one that I really enjoy undertaking, as all sorts of information pops out of the woodwork when the files are found!