Abstract: A firearm includes a barrel having a breech end. An upper receiver is engaged with the breech end of the barrel such that a majority of the barrel is outside of the upper receiver. A lower receiver is releasably connected to the upper receiver, and the firearm includes structure for slidingly connecting the upper receiver to the lower receiver.

Abstract: An alignment aid that includes a surface that defines a plane. First, second, and third references are aligned along a first axis of the surface, wherein each reference has a length along the first axis and a width along a second axis orthogonal to the first axis. A distance is between adjacent references along the first axis. Each reference includes a first alignment feature adjacent to a second alignment feature. Each first alignment feature has a first alignment feature elevation orthogonal to the first and second axes. Each second alignment feature has a second alignment feature elevation orthogonal to the first and second axes. For each reference, the first alignment feature elevation is higher than the second alignment feature elevation.

Abstract: An alignment aid that includes a surface that defines a plane. First, second, and third references are aligned along a first axis of the surface, wherein each reference has a length along the first axis and a width along a second axis orthogonal to the first axis. A distance is between adjacent references along the first axis. Each reference includes a first alignment feature adjacent to a second alignment feature. Each first alignment feature has a first alignment feature elevation orthogonal to the first and second axes. Each second alignment feature has a second alignment feature elevation orthogonal to the first and second axes. For each reference, the first alignment feature elevation is higher than the second alignment feature elevation.

Abstract: A firearm includes a barrel with a muzzle that defines an aim point. A front sight includes a front sight indicator. A rear sight includes a rear sight indicator. When a user extends the firearm toward a target and below a line of sight between the user and the target, the front sight indicator is visible to the user when the aim point of the firearm is above the target, the front sight indicator is not visible to the user when the aim point of the firearm is at or below the target, the rear sight indicator is visible to the user when the aim point of the firearm is below the target, and the rear sight indicator is not visible to the user when the aim point of the firearm is at or above the target.

Abstract: An alignment aid that includes first, second, and third references aligned along a first axis. Each reference has a length parallel to the first axis and a width orthogonal to the first axis. A distance between adjacent references increases along the first axis. In particular embodiments, the length and/or width of each reference may increase along the first axis. Other particular embodiments may include parallel lines aligned parallel along the first axis and/or a contrast on each side of each reference.