At high evolution levels (I've tested 0.998) and high artillery shell damage research levels (mine was at 9) the artillery fires two shells at one nest, despite killing it on the first nest.
the nests have 3484 health and the artillery's displayed damage with normal shells is
1.0k + 900 Physical
1.0k + 900 Explosion
It only does this if it can fire the second shell before the first shell hits, so at longer ranges.
For worms, the behavior is different. It fires one shell per worm.
[2.0.32] Artillery fires more shells than necessary to kill a biter nests
Re: [2.0.32] Artillery fires more shells than necessary to kill a biter nests
So in your case the physical damage is 1900 and explosion is 1900. Spawner has resistances Explosion 5 and Physical 2/15%. That means the effective explosion is 1895 and effective physical is 1613.3, total damage is 3508 hit points. Spawner has 3484 health points at this evolution factor. It is indeed going to die in one hit, but before the projectile hits, it registers as having 3508 predicted incoming damage. That is 0.6% more than full health but it is less than 5% of the "overkill" fraction set for biter nests. I see that in case of a single projectile dealing enough damage to kill an entity there is no chance any type of healing could interfere with entity damage process here, but that would be some amount of extra corner cases to handle. I am going to claim this is not a bug since when second projectile is fired, it does not know that the 3508 hit points of predicted damage comes from just a single projectile and not from a pair of projectiles that would arrive at different times making entity healing to possibly heal the spawner just enough so it would survive. When you reach next level of artillery shell damage, one bullet will deal 3693.3 hit points which is 6% more than max health meaning it will be above the overkill fraction and only one projectile will be fired.
