Question on Blackhawk Cylinder

I bought this 357 cylinder some time ago and never noticed these markings.
What are they?

Looks like foreign proof marks. It looks Italian, proof house Gardone.
FT44

Thank you. I wonder how it ended up in the US.

many times, guns, as well as parts, get back into this country either by importers,buying lend lease or other countries guns, recall many Rugers over the years getting sold to foreign countries, and they had to be "proofed" upon arrival in said country, as well as often guy ( gals) stationed in Europe can and will often buy a gun while "in country" or maybe even the base PX, base PX guns are NOT "proof marked" as it is US property....we've gotten guns from Belgium, italy and England from military personnel and these PX bought guns have ont been proof marked in all we've ever dealt with in all these years.........these guns will usually be seen with a green card signed by the commanding officer........
as for
parts', whole different set of findings.............proof marks can be found in the back section of any of the Blue books

Not really a "Blackhawk Cylinder" though ....?

Not even Ruger is my guess. An import for sure.

I agree, I would bet it's not a Ruger.