World download and screenshots can be found in the link below. This is a skeleton turret that reloads automatically when the skeleton has been killed. Skeletons are fed into the turret "magazine" from either a skeleton spawner or mob spawner if you have a reliable sorter. All redstone is concealed and turret is tileable.
Dang, I forgot I posted this, so never checked the replies! Well in the off chance you're still out there and wondering, the skeleton is on a pressure plate that is cleverly snugged into the surrounding redstone.
Here's a longer video that I posted on a dedicated Minecraft YouTube channel that I've since set up: