記憶にないなあ、そうだっけ？
https://www.stagezeroshooting.com/blitzkrieg-9mm-hydraulic-buffer-system.html
上のはAR９用の油圧バッファーだけどこんなのか？
https://www.defensereview.com/hydraulic-recoil-buffers-for-the-tactical-ar-15m4m4a1-carbinesbr-friend-of-foe-from-the-enidine-recoil-buffer-to-the-kynshot-recoil-damper-and-crosshair-buffers/
http://bulletin.accurateshooter.com/2010/04/new-hydraulic-buffer-for-308-win-ar-10-style-rifles/
当然AR15/10用にも油圧バッファーはあるけどさ