is there a point where it is not safe to use a bullet anymore? or a point where the accuracy or speed is greatly affected.

Are you talking loaded ammo or the bullet to load ?
If you are talking loaded ammo ,I am shooting up some 8mm ammo that was loaded in the late 40's still shoots great.

I have loaded bullets for chucks that have sat around gramp's shelf for 20+ years with no loss of accurey

So if you keep the ammo or bullets in a dry area ,it should be good for many ,many years.

Yeah, you'll get further and folks should understand better if you use correct nomenclature. The 'bullet' is the projectile only, the part that gets on out there. 'Cartridge' or 'round' is the whole thing: case, primer, powder, bullet.

I think I'd add 'cool' to johnch's 'dry' for storage.

Someone once gave me a coupla handfuls of .38 rounds, no idea how old they were or how they had been stored. I guessed them to be from the '50s, just based on what I knew of the giver. They shot lousy. All over the target. And it wasn't me, because every other group with the same gun at the same shootin' session was OK.

Last summer I shot a few Rottweil 20 ga. slugs. I had bought about 4 boxes from a guy at a gun show. Again, no idea on age or storage, but same results. They shot lousy.

Just store carefully and keep that stuff movin'. Shooting up the old keeps you in practice, too.

If the ammo is made right, and is stored in a dry place, it will probably be good indefinately. I've shot a lot of surplus ammo that is over 60 years old without any problems due to the age of the ammunition.

Storage is the key, dry storage, not subject to the temperature swings of the normal outdoors allows ammo to remain safe for many years. Large swings in temperature is hard on the powder inside the case, and moisture causes the cases to corrode, increasing the likelyhood of a seperation under full pressure. Plain old projectiles (bullets) wouldn't be affected by temperature swings, but corrosion can occur in both jacketed and cast lead examples.

Had some 60yr old surplus ammo from Pakistan . I had alot of clic-bangs/hangfires and duds