Hammer & chisel engraver (no air assist engraving tool used).
You can see and tell the difference in the tiny hammer facet marks left in the cuts.
..Though there are some air assist tools that can now mimic even that look with a bit of adjustment. Then a really careful look for changes in cadence of the hammer strokes gives it away.
The entire pattern was cut with a single tool,,a V shaped point. It is held straight up for the finest cuts and tilted either way to increase the width or flare of the cut.

Engravers each have a favorite angle they like to the tool. Most start out using a standard 90* tool. Those are simple as they are already set if you use standard tool steel blanks as gravers. Many stick with that included angle.
Some like a wider angle like 100 or even a bit larger 110*. Others a narrow point down to 80* even less for general work.
My standard go to, works on everything graver is 70* included angle V point and the face is ground at a 50* angle. A very slight heal on the bottom completes the shape and it's ready for work.
Probably something quite similar was used here. Perhaps a wider included angle on the tool.

The background was punched in with a very small most likely circular dot punch. Or maybe just a small flat point with the tip matted by tapping it on a fine file or even polishing paper to dull it..

The shading is with a 'liner tool'. A single tool that cuts multiple parallel lines. They come is a unending number of widths and # of lines per width. So just about any type of effect can be given. They are used for lettering, background removal and effect, modeling figures and more.

In using them for shading effect, it's considered less than top notch work over the use of a single point tool to cut individual shade lines.

That latter type of work can be of converging lines and varying width and add a lot to the art,,,and the amt of time spent and then the final cost of course.
Single point shading takes a lot of time. Use of a liner is very fast.
..Not everything is a museum centerpiece nor meant to be.

I don't know a lot (much of anything actually) about factory work, but it does appear like that of the type shown to me and said to be the work sent out to Italy for engraving by the Factory in the 80's(?).

I see where you have found some paperwork that seems to confirm that along with RK's valued opinion.
Very nice revolver!
A confirming factory letter will be a nice addition to it.