Technically, it would be sufficient of they lodge a bullet into the barrel. As soon as the tank fires, the bullet will wedge between the shell and the barrel, destroying - at least - the barrel.
You’d have to be pretty lucky for a bullet to enter from the front in a way that it wouldn’t just get blown back out by the shockwave before the shell reaches it.
Technically, it would be sufficient of they lodge a bullet into the barrel. As soon as the tank fires, the bullet will wedge between the shell and the barrel, destroying - at least - the barrel.
You’d have to be pretty lucky for a bullet to enter from the front in a way that it wouldn’t just get blown back out by the shockwave before the shell reaches it.