Those 100 lb runt pigs that are 150-180 lbs behind the group will eveeeeeeeeeentually get big if you put feed in front of them long enough.

They will likely celebrate at least one Birthday.

As for butchering them at 100 lbs, for the most part the cost of having it butchered is going to be too much for what you get.

If you want to feed a few you probably should have cheap feed available and go into it thinking it is a learning exp, not for profit.

Grass alone will be very slow growth.  If you have some waste feed from other animals that would work good as long as there aren't any meds in the waste feed that shouldn't go to hogs.

If you have kids it could be a good summer project for them.