Here's the deal on engraving with a CNC on curved surfaces like barrels or receivers.
On a 1.200 to 1.250 OD barrel cylinder your limited to around .750 to .825 of vertical space on the artwork. It has to fit in that work envelope otherwise you lose the effect. You want to be able to look at the engraving and instantly recognize it. If it's larger you end up rolling the gun or your neck to see it all and the whole idea goes away.
So, scaling the artwork becomes very important.
Scaling is easy, but its a double edge sword. If you send me a big ol JPEG or your chosen artwork, say a piece of "toon art" like Betty Boop (cuz she's hot!).
By the time I get Betty to fit in that vertical window she's going to look like a steel silhouette hammered to shit because any detail is going to washed out by the width of the engraving tool. At .003 to .005 depth its roughly .008 to .01 wide. Smaller tools do exist but they are a bit cranky to use as they erode so quickly. That and you need a zillion RPM on the spindle to use them that I just don't have. (20-40 K works nice)
-On that note there is an air driven Yuasa Cat40 spindle adapter that I used once that'll go to 100K but the noise is deafening. Bout like standing next to an F-4 Phantom on take off (my favorite jet as I grew up watching them take off all the time)
It's taken years of practice and dickering with this stuff to be able to dilute a piece of artwork to where it'll engrave and still deliver enough detail to send the message.
Fonts like Old English or heavily scrolled stuff also gets a bit "mushy" unless they are really big. Not much I can do about it when most character heights are .100".
Just stuff to consider.
C.