This is a personal experience - not to be relied on in other situations.
I locally purchased an antique 38 caliber revolver. I had my "stepson" do the paper work.
After submitting the weapon to the local army base and completing dozens of forms. (while lying about the source of the revolver), the pistol became legal in about 40 days.
I am not a gun nut, but locally in beautiful downtown Catemaco, Veracruz, if I want, I can purchase anything I might want, subject to waiting periods, possibly excluding rocket launchers.
And that consistently surprises the hell out of me, knowing the extraordinarily tough regulations of gun ownership in Meico.