If you feel like your grip isn't strong enough to apply sufficient pressure with the basic KAMsnaps pliers, here's a tip.
Rather than holding the pliers in your hand, rest the bottom on a table instead. Then, press down on the top handle of the pliers. You can use your other hand to help. This will provide better leverage so you'll be able to apply more pressure. Like this:
This is similar to how holding a stapler will make a difference. Imagine holding the stapler in your hand to staple something. You have to rely on the grip of your hand to do all the work.
Now imagine placing the stapler on a table and then stapling something. In this case, you're just leaning into the stapler and pushing down with your arm. No hand grip is involved.