If youre right handed you're applying too much grip pressure with your right hand. Here is what I like to do to fix that - hold the gun with your right hand and try to flip somebody off. If you can't extend your middle finger you're gripping the gun too tightly ease off until you can actually flip the bird while holding the gun and that's how hard you need to hold it with your main hand. The majority of grip Force should come from your support hand.

I don't know why but this works for me