its very weird that all of the links to buy things are from the same literally-who tier gun site. maybe im cynical years of seeing shills on /k/ (fucking Special Weapons for like a goddamn decade before it went under, thank god), maybe its completely innocent, but it just strikes me as weird.
in any case, a .44 magnum (or a .357, or almost any handgun that isnt, like, a fucking heap of rust or some homemade bullshit) WILL act as a fantastic way to CTB. you have to angle the barrel at either just behind your temple, at your brain stem, anything like a .22lr i wouldn't bother (hah, thank god this isnt a gun forum, some angry boomer would be really mad at me for putting down the almighty .22). a medical diagram of the brain actually helps a lot with this.
rifle calibers also work well. ive seen so much footage of people accidentally offing themselves with 5.56 ar platform guns, ak varisnts, and even one spectacular one where a dude shot himself in the head with a black powder muzzleloader. shotguns are the *best*, but not the only.
the BIGGEST issue one may run into is ammunition. do not buy literally-who tier brands as you will risk FTFs (failure to fire) or hell, even the round just blowing the fuck apart upon leaving the barrel. i had that happen with some cheap bullshit .22 ammo once when trying to kill a venomous snake. no thanks. you want a good, clean ejection, not fragmentation that may not kill you. spend money on more expensive, more reliable ammunition. avoid, in particular, ANY ammo made by Monarch. also be dubious of anything marketing itself as "military grade". zack hazard has several videos describing how even a basic bitch walmart ar is in better condition than most of the militaries guns and how military grade is just a cashgrab term. he was in the GWOT, he was a small arms repairman, i trust his word over most other guntubers.
in any case, have a good night.
edit: attached is a diagram that will help in locating the brainstem.