nothing will work your grip like judo itself.
hmm Ive gotten alot of mileage out of a med ball
A hammer requires two things- the sledge and a thing to hit.
a med ball one less thing but you might need to do a shit load more
med ball work then hitting a log or tire with a hammer.
Im not just thinking slams- passes etc- but using the med ball
sit ups - pushups - assisted stretching leg lifts- hugging it
hold a med ball in a head lock for a few minutes and youll develope some good squeeze
while slams would be my favorite- but you have to pair them with something.
pullups - hand stand pushup etc
that being said I do enjoy hitting shit with a sledge quite a bit.
Using a pick axe or Adze is even better.
Judo + Manual work has given me a solid grip well into my mid 40's
so if you get in enough hours on the mat grip will eventually take care of it self.
big hands help here, as do big wrists and big forearms.
yes some of that is genetics - but allot of it is from work/hours/reps
big note on grip - when your conditioning is weak your grip will fatigue much much faster
they are tied together
as for working with bands - its a partnerless way to get some rhythm down.
as for rotational development-
hammer swings feel like they help
Ive tried a ton of different ways to develop rotational power in the weight room
Its not easy- lots of throwers ( discus hammer ) work on that too - twisting doesnt help
plain jane stuff really works here.
I found heavy ass cleans
cleans pulls snatch pulls off blocks really good
all to really work
some surprising shit that worked way way more then I thought
reverse lunges ( barbell front squat rack)
trap bar carries/farmers carrys
or suit case carry ( one arm)
air hump glute bridge
a massive amount of 'core' ab and low back work
hanging leg raises
BB roll outs
and some secret grip Pchain blowout
continous snatch width dead or RDL or dimmel style deads for sets of 20 or 30
will blow up your grip and pchain.