exactly. Just wait until they have to get rid of the grenade. its not like the snake is going to time it exactly right before we chaingrab.i dont think you can cook a grenade when your in the middle of gettign CGed. any smart player wont CG snake or link or w/e else when they have an explosive in their hand. thats just plain stupid if you do that. he will also take alot of damage when the grenade goes off if you decide to do that
And the up to 70% isn't all chaingrab (at least I don't think so...), it also involves following up with an aerial combo after you think the damage is too high to keep FP'ing. At least thats what I do. Following up with an aerial combo is much better than FP'ing when their % is fairly high, then having them DI away from you and get their ground back.
When you think the FP chaingrab is about to 'run out' because of knockback/DI, immediately follow up with SH > fair > nair. So satisfying. Then you land in the middle of nair, in which you get zero lag.