I have punch stamp sets in various sizes that work well with practice and patience. Proper set up is key. (Solid table and a good solid backing depending on the receiver type.)
There are other better options out there. Trophy shops that are gun friendly can do it for you as well.
I have seen a lot of laser engraving recently which certainly looks best. I thought according to the ATF marking requirements that laser was a no go, but now that manufacturers are using it, the standard must have changed. No known source for that info though.
Just make sure you write your full trust name (you can not shorten it) and your town and state.
Make sure you have it marked before your form is approved, because once it is approved, you MUST be present when they are marking it. You can not leave it in anyone's custody unless it is a SOT, which requires more work for them. Better to just do it right the first time.
Per ATF:
" The
requirement that the marking be “conspicuously” placed
on the firearm means that the marking must be
wholly unobstructed from plain view. For firearms
manufactured on or after
January 30, 2002, the serial
number must be to a minimum depth of .003 inch
and in a print size no smaller than 1/16 inch. "
(3) The manufacturer’s name
(or recognized abbreviation)
(AGAIN, CANNOT DO THIS WITH TRUSTS!); and
(4) The city and State (or recognized abbrevia
tion) where the manufacturer maintains its place
of business.
122
7.4.3 Measuring the depth of markings
. The depth of all markings is measured from the flat surface
of the metal and not the peaks or ridges. The height
of serial numbers is measured as the distance
between the latitudinal ends of the
character impression bottoms (bases). "
Source:
https://www.atf.gov/file/58221/download