I wonder if a maker had to be a member of the Worshipful Company to have his guns proved in London.Others will know more about this than me. I noted a number of Scottish makers who sent their guns to London
for proofing, when Birmingham would have been closer, no doubt for the perceived cachet. For a London maker to send guns to Birmingham would have meant extra expense and administration plus increased risk of damage or loss.
Even if Reilly did not make the actions he would still have to proof the gun when the barrels were fitted, if he intended to sell the gun. With 300 employees you would think he would have been delivering guns for proof each week and picking them up to bring back to the factory for careful cleaning, as the London proof house did not clean the guns after proof, according to some records concerning the Colt Agency in London prior to 1913.