Just a little more 'back-story' to the problems with American manufactured ammunition :
During WW1 around 50% of the 303 supplied was deemed 'not fit for use' and was relegated to practice use only, add in the fact that by 1916 the 3 American suppliers to Britainwere over 400,000,000 (400 million) rounds below their promised delivery rate.
The decision was taken to cancel all contracts with the US at the earliest opportunity.