Skinny forearms are a big problem if shooting off bags regardless of weight. Lots of light rifles also come with skinny forearms. They tend to want to roll to the right due to your face pushing to the right, and your hand pulling to the right on the trigger. Shooting a pistol really helps with trigger technique of pulling straight back.
One solution is a bipod to stop the roll, but light guns tend to bounce more during the shot, so so you have to reset between shots. On my light guns I'll often run two front sandbags in front to stop the roll.
