I had a Hy-Score Sporster here for repair, so I thought I would snap a few pics while it was apart. For those that have never had one of these little pistols apart, a few things that tend to "buck the norm" are readily noticeable.

One of the more unusual features, for any spring gun, is the presence of a lubricating wick on the piston head. The next thing that becomes apparent, in spite of being a concentric piston action (barrel runs throught the center of the piston), there is no seal present between the ID of the piston, and the barrel - just a very smooth, close tolerance hole through which the barrel passes - the lubricants form the seal. The piston head is fastened to the skirt of the piston in a manner that allows the head to "float" - no doubt to help maintain a seal. The spring guide also "floats" within the confines of the mainspring ID. The gun uses a common O-ring seal on the piston head, and a proprietary seal within the rear end cap, which seals the main compression tube, so that all the compressed air is directed to the breech, and thus to the pellet. This particular gun suffered from a deteriorated end seal, and a fatigued mainspring. While it was still in pretty good shape, the piston seal o-ring was replaced simply out of good practice.