I travel to Mexico regularly and have a copy of a Mexican government publication of their firearms and ammunition laws. (written in Spanish of course). Short version, .38 super and .45 ACP are prohibited calibers, as are 9mm Luger, .357 Mag, .357 Sig, .40 S&W. For civilian ownership, the most powerful cartridges allowed are .380 ACP and .38 Special. You can own a revolver chambered for .357 Magnum but you are only allowed to have .38 Special ammo for it. .22's, .25's, .32's and .380's are all common. Yes, .38 Super is popular down there but is a prohibited cartridge for civilians. You can get a permit to bring a gun into Mexico for sanctioned shooting competitions and hunting. Foreigners cannot get carry permits. Carry permits for locals are very rare, but legal ownership of guns is more common than most people think.
In case you are curious, all semi-auto rifles except .22 rimfires are prohibited and in rifle cartridges .223 and 7.62x39 are prohibited. I would have to check to see if .308 Win. has been taken off the prohibited list. (it is on the list in my book but it was published 10 years ago).