The contract was also printed in the Thomas Mifflin papers but I confess I hadn't seen the original.
It was never fulfilled. There have been several references to it in secondary sources that say it was cancelled by the British government. I have reservations about that, though not in effect. I don't think the government cancelled it. It is much more likely that they refused an export license which ALL overseas shipments of British arms required, even if they were going to British colonies. I have not found out why and likely can't until I can get into the microfilm of the Rufus King papers in the Massachusetts Historical Society. King was the US charge' de affairs in London that handled the transaction for Gov. Mifflin who corresponded with the pertinent British officials through him. Mifflin's papers contain a report to the Pennsylvania Assembly that the British Government effectively nullified the agreement. My guess - which I will not publish unless I can prove it – is that Pennsylvania balked at posting the bond required for an export license by the Privy Council. This was six times the value of the cargo, which, for a contract like this would have been a stupendous amount of money...they may not have had the means to do it because the bond would have to have been posted in London.
All exporters posted the bond... When the State of New York and the US Government purchased muskets in Britain, they bought them directly from the British Ordnance Office. I am not certain that the Ordnance Office was subject to Privy Council licensing in this situation but otherwise they were certainly exempt under the 1757 law that required the licenses. The Privy council regularly refused licenses for the export of "muskets with bayonets" until after the New York purchase at which point they wrote to the Ordnance Office to ask if such sales were now permitted. Again, I haven't found the reply to that question and won't be able to until I can get back into the British Archives but it is clear that after the New York sale, muskets started to be sold to America.