Note: Getting an accurate HP count is difficult because of the constant spawning of spiders.
Mother Spiders have a spawn limit. I found that out while my "lets play" in E4L6.
And this level is easy to do it occur.
-> Go to the spider key where 3 mother spiders are (at least on extra crispy skill) -> Let one Mother Spider follow you the way back where you came from. Lead it further and further. You'll notice that she'll stop spawning spiders after a while. Go further back with her. It should be easy to avoid their babys because the way back there are a lot of staircases and other obstacles for the small ones. So you should manage to get alone with her. Now you should be able to get their HP Amount. Never load the game though - if you load the game it will spawn spiders again!
I unfortunately dont know the way how you measure the HP of the enemies. 1st) I dont know the damage each weapon does, and 2nd) most enemies have special resistance / sensibility to specific weapons - Hell Hounds are for example very stable to explosions and invulnerable to fire, while flesh gargoyles seem very sensitive to tesla and stone gargoyles seem very sensitive to voodoo doll primary fire. And so on. You sure know this. So I wonder a bit in general how you measure weapon power and hp of enemies?