You know the one on 3 gun shot guns and on the shot gun in John Wick? I’ve tried my damndest to google these things. Just a piece of plastic or rubber that you stick to the receiver of your shot gun right by the ejection port so you can slide a shell in really quick if needed

Match saver is what I've heard them called.

Matchsaverz shotgun shell holder.

Yep. You run dry, you swipe it back into the port and hit he button. Works well.

That’s it, thanks