When I'm shooting smaller revolvers off the bench I use a rear bag for a rifle turned over so I have a smaller area of the bag on top. I rest the front of the trigger gaurd on top and press my buckles into the bag. If there is a mechanical issue causing groups that large a thorough inspection should show a problem. If you don't see anything wrong like jacket shavings from timing issues or a bad crown keep practicing. It doesn't take much sight misalignment to make patterns instead of groups at 50 yards. If you're just getting into handguns I wouldn't call that terrible shooting