Hello, My son has a Umarex Ruger 10/22 that the o-ring on the cylinder that pierces the co2 cartridge has gone bad or over tightened. I reached out to Umarex to find out it is no longer made. Being that the o-ring disappeared as well I'm wondering if anyone has the correct size of it or where I possibly could find one. Umarex was no help. Thank you!