If you have ever taken apart an old vintage Daisy 880 or similar variant then you have probably experienced the mess that is the elastomer spring on the piston assembly. When the elastomer breaks down it leaves a nasty black mess in the compression tube. The remains of the elastomer can be a challenge to remove. Then there is the installation of a new elastomer. IF all goes well it installs with no fuss, BUT sometimes it is a smidge too long and when compressed after assembly it bulges out too far and will not fit in the compression tube. When that happens the elastomer must be trimmed shorter so that it will no bulge out too much to fit in the compression tube. If it is trimmed a little too much then it will no push against the piston as strong and will hurt performance. The 880 community has had to live with that for decades, that is until the 1977 was released. A 1977 piston assembly uses a flat spring instead of the elastomer. The 1977 piston can be ordered from Daisy for $10. Just a few more dollars than the elastomer spring. It turns out that the square spring can be removed from the 1977 piston assembly and installed on a 880 piston assembly. When installed on the 880 piston assembly the spring is compressed 1.5mm more than when installed on the 1977. The spring will obviously not "melt" over time like the elastomer and will hold up to a wider variety of oils. I have linked a video of a vintage 880 rebuild where I installed the 1977 piston spring, the spring is covered at 6.25 minutes into the video.