A firm grip on the bow will lead to torquing the bow more and more with each successive shot, due to fatigue. If you are fresh and start shooting, you might not see it reflected in your shots, but it becomes more noticable the longer you shoot.

Plus, think about this. Most shooters start out at the shortest distance during their practice session. In other words, you go get your bow, walk out 20 yards and begin shooting. After a couple of rounds you move to 30 then 40 ect....... So as you are getting more tired, you are also moving back in distance. It is at this point that the shooter can see his groups starting to open up more and more. You are fatigued, you have moved back more and more, and your grip is torquing the bow. That is what happens, and yet people don't understand why the groups open up.

But if you practiced in reverse, start at 40 , then 30 , and finish at 20, you would still suffer fatigue, and you would still be torquing the bow, but at only 20 yards, the distance is short enough that the shots cant open up as before, and you would think you were shooting great.

The farther the distance, the more your form issues get amplified.

Hope this explains it a bit.

And to answer your question, No , you should not have a firm grip. Basically, you should have the last 3 fingers open, withthe thumb and index finger wrapping the grip to touch. Not any tighter.

Good luck.