I have the bullet, now I just need to make some contraption to fire it into my head, please help me out...

its harder than you think to angle it

You are going to end up as a vegetable and unable to finish yourself off. Get a better plan or don't do it at all.

Ask k you just need a tube that fits, if it's metal it'll probably take the pressure

Looks more like .22 Short. Even better.
Yeah, OP, totally do that to yourself.

FYI that probably won't kill you

Try something bigger. You wanna make sure it absolutely destroys your brain. Say for example, a shotgun shell w/slugs or something like that

dont even bother, if you're gonna do it use a real bullet

its a long, should probably wouldn't kill me

Dont kill yourself, you want succeed with that. if you do somehow die after the agonizing pain of bleeding out if it doesn't immediately kill you, You'll find yourself viewing your dead corpse in the void, and you will be disgusted and ashamed at yourself, because you will soon find out that the future choices you could of taken could have led you to a life of immortality, the techniques known to the masters that lay the fingers of death off past 200 years. You will feel great regret and spend the next perceived years in a strange and dark place, and without knowledge you won't be able to navigate it/fend of the malicious entities that lurk there.

It’s about velocity, you’re shitty pipe gun is gonna push that thing so slowly that it will do minimal damage.