I'm not taking sides - I'm only looking at Roys letter, and trying to understand it.
If Roy thinks the factory stopped using alloy cylinders after a certain date, and
switched to steel at that time, then that is what is going to be in the letter.

I doubt the invoice records say anything about the cylinder material. The factory
letters reflect what is in the invoices, and what is in the various manufacturing and
engineering records. All the letter reflects is an interpretation of the available
information.

Perhaps you should call Roy, and ask him why it is that the gun letters with a steel
cylinder.

Regards, Mike Priwer