Crossbow is not made to kill crabgrass but I have killed some crabgrass by using crossbow.
However if you really want to kill crabgrass you can use bleach or vinegar, salt and dish soap or pour some diesel fuel on the crabgrass.
Or buy a crabgrass killer to kill the crabgrass.
A good crabgrass killer is the Drive XLR8 crabgrass killer.
You can also use the bleach to kill other weeds.
Yes bleach can and will kill weeds.
You can pour or spray some undiluted bleach on the weeds and the undiluted bleach will kill off the weeds.
You can use bleach to kill off weeds that are also growing through cracks of concrete or pavers and the bleach will start killing the weeds within a few hours and within 24 to 48 hours the weeds should be fully dead.
I pour bleach in cracks of the pavers and cracks in concrete where the weeds are growing and it kills them and the bleach also helps prevent the weeds from growing.
You can also use vinegar, salt and dish soap to kill weeds as well and it's an environmentally friendly weed killer.
Diesel can also kill weeds and even old used motor oil.