Argo44

I really respect the amount of original research you have undertaken on the firm of E M Reilly, especially in running to ground lots of newspaper notices with advertisements and address and so on.
Coming back to the subject of whether E M Reilly made his own guns.
One source which may provide some definitive evidence are the proof day books for The Worshipful Company of Gunmakers, London proof house. These are held in the library of the Guild Hall in central London. I have gone through some of these myself mainly for the periods of 1914-1918 and 1940-1945, also in connection with research I am doing on guns made by Vickers and Vickers Armstrong. I don't have the full date range of the ledgers to hand, but if you pick a period of time that you feel certain Reilly made guns not using Belgium tubes and the day books are available, then the name of Reilly will appear in those ledgers.
If not some other maker made his guns. With Reilly being based in London in would be natural for him to use the London proof house, rather than Birmingham.

Regards

AlanD
Sydney