So here's a try using just one Illustrius checkpoint.
The prompt was:

score_9
,score_8_up
,rating_explicit
,BREAK
,debreast_mutilated
,toxra
,corpsexl_injury_art
,guro
,BREAK
,(open cuts:1.25)
,(streams of blood:1.2)
,(damaged_torso:1.275)
,(mutilated breast:1.55)
,(blood:1.2)
,(blood splatter:1.25)
,(splatter:1.25)
,(gunshoot holes in her tits:1.45)
,(firearm wounds breasts:1.45)
//,BREAK
//,disembowel
//,injury
//,bad end
//,(mutilated breasts:1.1)
//,bleeding
,BREAK
,(extreme wide flesh:1.15)
,(blood spray:1.35)
,(blood mist:1.25)
,(bleeing:1.25)
,(gib:1.2)
,(deep wounds:1.3)
,slashed_body
,(mutilated:1.3)
,uncensored

I used the following as a checkpoint: waiIllustriousSDXL-v17

As you can see, I think the result is even worse. Maybe you could tell me which checkpoint you're referring to. And maybe this isn't entirely clear, but I do want the breasts to have deep gunshot wounds—or even to burst open completely. The same goes for the head, by the way.