A 20 gauge with a full choke barrel shooting shot charges can be effective out to a maximum range of 40-50 yards. A slug shot from a 20-gauge slug setup may be effective out to 100 yards. But for the majority of shots from a stand, you will want to be able to reach at least 25 yards. When shooting from a standing or sitting position, you need to consider how far it is to the target and whether you have enough time to get there. If you are facing a large animal such as a elk or a bear and don't have any cover between you and them, then you need to think about how close you can get before they realize you are a threat and take off. This distance depends on many factors such as what kind of sight you have, if you are using optics, and how fast the animal is moving. But generally, you want to give yourself enough time to take your shot and still run if needed. For example, if you are sitting in a tree stand and the deer walks within 10 yards of where you are sitting, you won't have enough time to take your shot if you aren't able to shoot very quickly. In this case, you should consider moving to another location within easy running distance so you have more room to maneuver if needed.