When using the air grease gun you can't rush it, you have to let the pistone to return before you push the trigger again. I always use a leather glove on the hand that is on the end of the hose, had a friend have one explode in his hand and filled his hand with grease. He almost lost his hand from infection, he recovered bur his hand is a ugly mess. They can put out upwards of 10,000 psi depending on the air pressure going to it.
