> For example the 5N7 5.45 AK-74 bullet, the "poison" one, had an air-pocket in front between jacket and the core.
This is actually common on a lot of rifle bullets. Search for OTM or open tip match. There are some open arguments in the gun community about it's effect on ballistics etc, but it actually comes from a by product of the manufacturing of the bullet. Most FMJ bullets have the copper skin formed so that it's open in the back, OTM bullets are "backwards" and are run through a form after the lead is poured. This shrinks the area of the opening in the shell and pushes it to the center. Which makes it easier to keep things radially concentric and balanced. Something that's very important at longer distances.
This is actually common on a lot of rifle bullets. Search for OTM or open tip match. There are some open arguments in the gun community about it's effect on ballistics etc, but it actually comes from a by product of the manufacturing of the bullet. Most FMJ bullets have the copper skin formed so that it's open in the back, OTM bullets are "backwards" and are run through a form after the lead is poured. This shrinks the area of the opening in the shell and pushes it to the center. Which makes it easier to keep things radially concentric and balanced. Something that's very important at longer distances.