Gasses from a revolver actually escape at the front of the cylinder, through the cylinder gap between the cylinder and the forcing cone at the ear of the barrel proper. Putting your finger or thumb (or whatever) across that area WILL result in serious injury. If you have gas escaping the rear of the cylinder, I recommend you see a qualified gunsmith post haste - and stop shooting that revolver. As for proper grip, there are any number of illustrations and demonstrations to be found. My preference doesn't differ much from my two-hand auto grip.
You Have enemies? Good. That means that you've stood up for something in your life. --Winston Churchill
The right to buy weapons is the right to be free. -- A.E. Van Vogt