I have been following this thread with interest, especially with respect to the British orders for Serbia, so I though I would post a few details to help with some of the conjecture.
For the first few months of the war orders placed in the United States by Britain were placed directly by the War Office, but from January 1915 a new system was instigated. J.P.Morgan were appointed as the British Purchasing Agent in the United States with full authority to place contracts and negotiate with suppliers. This continued after April 1915 when the Ministry of Munitions was formed under Lloyd George
Surviving records of these contracts are pretty good, but I would add the caveat that they are not 100% complete and I have found a few omissions and errors.
There is no record of any British contract with Western for 7 x 57mm ammunition, neither with Western direct nor their UK representative, N.G.Prince. However, a contract was placed with Remington and part or all of this contract may have been sub-contracted to Western. This would not have been unusual, as the British government placed a number of contracts with Remington as agents, for example the .455 pistol orders from Smith & Wesson.
The contract with Remington was part of an order for 159,800,000 rounds of .303 ammunition placed under C.1545 dated 12.2.1915 which stated “40,000,000 7mm cartridges are to be delivered in lieu of similar quantity of .303; deliveries of .303 not to be affected except during period 7mm is being manufactured.” This contract was due to be completed by 1.5.1916 but records show that only 2,200,000 had been delivered by March 1917 and Morgan’s were awaiting proposals from the contractor.
With regard to the chargers for the 7mm Serbian cartridge, Hinks Wells in Birmingham were given contract 94/C/1165 dated 25.11.1915, with two following contracts in 1916 for a total of 8,000,000 chargers which is shown as completed. This matches the 40 million round order placed with Remington. Whether or not the Remington contract was eventually complted is not known, but it is possible it was and arrived too late to be sent to Serbia.
Incidently Peter, I have the British drawing of the Serbian charger but it is too large to post here. Drawing number is C.I.W. (Chief Inspector Woolwich) 2714 and it is undated.