There are lots of rounds designated 7.62mm, from Russian pistol and revolver cartridges, through the AK47 round, also the historic larger rimmed round still used in Russian machine guns (7.62 x 54R), but the most ubiquitous in the West is the 7.62 x 51mm, aka 7.62 NATO, which is a battle rifle/machine gun round, though it is interchangeable with .308 Winchester, which is (usually) a globally popular hunting round.
Even the venerable 30-06 US military round is sometimes referred to as 7.62 x 63mm
So first of all, what sort of rounds do you have ?
Whichever, it would be very difficult for you to fabricate an improvised device to use suicidally successfully, unless you have engineering facilities and skills.
There is a fixation on the forum about unsuccessful attempts with proper firearms, and a seeming belief that unless the medulla (brain stem) is hit, death is unlikely. These fears are wildly exaggerated, but just imagine just how much more likely this would be when attempting to use an improvised device.
Depending on where you live, possession of live ammunition without proper certification may be an offence, so consider this too.