Make sure the gun has absolutely no air in it when you try to take the reg off. This can be done by ensuring the breach is empty, turning the marker on, turning the eyes off and pulling the trigger a few times. If there's air in the gun, getting the inline reg off will be much harder.
If you want to set off and go develop some grand new thing, you don't need millions of dollars of capitalization. You need enough pizza and Diet Coke to stick in your refrigerator, a cheap PC to work on, and the dedication to go through with it. We slept on floors. We waded across rivers. -John Carmack