Somewhere, but don't remember where, I had read that a .22 LR achieves maximum velocity at 16 inches. The article said going more than a very few inches past that can harm accuracy due to more chances for movement or barrel defects. Many "precision" .22's I've seen have barrels around 18" and are going to use optics. If using open sights, a longer sight radius will aid accuracy, so it depends on what you are shooting if you want a longer or shorter barrel.